The three monotheist religious traditions, Judaism, Christianity and Islam, have more in common than in contention. All three believe God is one, unique, concerned with humanity’s condition. Each takes up the narrative of the others’ — Christianity and Islam carrying forward the story begun in the Hebrew scriptures of ancient Israel that define Judaism.

Christianity affirms the vocation of Israel after the flesh, and Islam affirms the validity of the antecedent monotheist revelations, regarding Muhammad as the seal of prophecy and the Quran as a work of God.

Falling into the genus of religion and forming a single sub-species of theistic religions, the three monotheisms among all theistic religions bear a unique relationship to one another. That is because they concur not only in general, but in particular ways. Specifically, they tell stories of the same type, and some of the stories that they tell turn out to go over much the same ground.

Judaism, with its focus upon the Hebrew scriptures of ancient Israel, tells the story of the one God, who created man in his image, and of what happened then within the framework of Israel, the holy people. Christianity takes up that story but gives it a different reading and ending by instantiating the relations between God and his people in the life of a single human being. For its part, in sequence, Islam recapitulates some basic components of the same story, affirming the revelations of Judaism and then Christianity, but drawing the story onward to yet another climax.

We cannot point to any three other religions that form so intimate a narrative relationship as do the successive revelations of monotheism. No other set of triplets tells a single, continuous story for themselves as do Islam in relationship to Christianity, and Christianity in relationship to Judaism. What demands close reading is this: Within the logic of monotheism, how do Islam, Christianity and Judaism represent diverse choices among a common set of possibilities?
The three religions of one God concur and contend. The basic categories are congruent, the articulation of those categories is not. By showing the range and potential of a common conviction — that God is one and unique, makes demands upon man’s social order and the conduct of every day life, distinguishes those who do his will from the rest of humanity and will stand in judgment upon all mankind at the end of days — the three religions address a common program.

But differing in detail, each affords perspective upon the character of the others. Each sheds light on the choices the others have made from what defines a common agenda, a single menu: the category-formations that they share.
What are the theological issues subject to debate?

• Does the interior logic of monotheism require God to be represented as incorporeal and wholly abstract, or can the one, unique God be represented by appeal to analogies supplied by man?

In line with Genesis 1:26, which speaks of God’s making man “in our image, after our likeness,” and the commandment (Ex. 20:4), “You shall not make yourself a graven image or any likeness of anything” in nature, what conclusions are to be drawn?

At one end of the continuum, Islam insists that God cannot be represented in any way, shape or form, not even by man as created in his image, after his likeness. At the other end, Christianity finds that God is both embodied and eternally accessible in the fully divine Son, Jesus Christ. In the middle Judaism represents God in some ways as consubstantial with man, in other ways as wholly other.

• God makes himself known to particular persons, who, in the nature of things, form communities among themselves. God addresses a “you” that is not only singular, a Moses or a Jesus or a Muhammad, but plural — all who will believe, act and obey. Islam, Christianity and Judaism concur that the faithful form a distinct group, defined by those who accept God’s rule and regulation. But among all humanity, how does that group tell its story, and with what consequence for the definition of the type of group that is constituted?

Judaism tells the story of the faithful as an extended family, all of them children of the same ancestors, Abraham and Sarah. It invokes the metaphor of a family, with the result that the faithful adopt for themselves the narrative of a supernatural genealogy, one that finds within the family all who identify themselves as part of it by making its story their genealogy too.

Islam dispenses entirely with the analogy of a family, defining God’s people, instead, through the image of a community of the faithful worshipers of God, seeing Muslims as supporters of one another and caretakers of the least fortunate or weakest members of the community.

Where Judaism speaks of a family among the families of humankind or of “Israel” as a nation unlike all others, sui generis, Islam takes the diametrically opposed view. Its “people of God” are ultimately extensible to encompass all humankind within the community of true worshipers of God.

Here Christianity takes a middle position. Like Judaism, it views the faithful as a people, but like Islam, it obliterates all prior genealogical distinctions, whether of ethnicity, gender or politics. So Christians form “a people of the peoples,” “a people that is no people,” using the familiar metaphor of Israel. At the same time, they underscore, like Islam, a conception of themselves as comprised by mankind without lines of differentiation.

• God has set forth what he wants from his people, which is the love and devotion of his creatures. This comes to realization in a program of actions to be carried out and to be avoided. These concern acts of prayer, study, contemplation and reflection on divine revelation (in the case of Judaism, study of Torah; in the case of Christianity, the realization and enactment of the image of Christ within the individual believer and the community; in the case of Islam, particular prescribed ritual acts of piety and worship: testimony of faith, ritual prayer, almsgiving, fasting, pilgrimage as well as recitation of God’s word, calling upon him in personal prayer and obedience to His will).

All three also require deeds of philanthropy in charity and acts of loving kindness, above and beyond the requirements of the law. Judaism and Islam share certain food laws (e.g., not to eat carrion but to eat only meat from animals that have been properly slaughtered), and Christianity in its formative age forbade the faithful to eat meat that had been offered to idolatry. Where Islam requires a pilgrimage to Mecca, the observance of the festivals of Judaism encompassed a pilgrimage to the Temple in Jerusalem when it still stood and Christianity portrayed all the faithful as pilgrims to the new, heavenly Jerusalem that God was preparing for his people.

In these and comparable ways, the three religions aim at defining acts that realize God’s will and that sanctify God’s people.
How is God’s people to relate to everybody else? What are the consequences of the conviction that the one and only God has made himself known to humanity at large through one community or person or family? Specifically, what is the task of the believer vis-à-vis the unbeliever?

At one end of the continuum, Judaism asks the faithful to avoid participating in, or in any way affirming, the activities of the idolaters in their idolatry. Amiable relationships on ordinary occasions give way to strict isolation from idolatry and all things used in that connection. At the other end of the continuum, Islam, for reasons equally systemic, takes the most active role, undertaking to obliterate idolatry by wiping out its worshipers.

Judaism in its classical statement defined its task as passive avoidance, joined with a willingness to accept the sincere convert. Islam called for active the extermination of idolatry, joined with an insistence that, to live, the idolater must renounce his error and acknowledge the one true God and his own.

Yet, early Islam took a very different position vis-à-vis Jews and Christians and a few other “people of Scripture.” These were to be largely tolerated so long as they did not threaten Muslims or the practice of Islam.

Christianity found its position in the middle. On one hand, like Judaism and Islam, Christianity forbade the faithful to utilize anything that could serve idolatry and to refrain, even at the cost of death (“martyrdom”), from all gestures of complicity with idolatry. On the other hand, like Judaism and unlike Islam, Christianity in its formative age contemplated not a holy war of extermination but an on-going campaign of evangelism, to win over idolaters. True, in due course, Christianity would slide over to the Islamic side of this continuum, but that happened many centuries beyond the classical age.

In its formative centuries, Christianity’s logic dictated a policy toward unbelievers that placed the religion in the middle, between Judaic passivity and Islamic activity.

• What of the end of days? Here is where the interior logic (as well as the articulation) of the three monotheisms both converges and diverges. As told in common, the story finds the resolution of the dialectic of how the one omnipotent and just God can account for a world of manifest injustice.

All three religions concur that God will bring the end of days, when all mankind will be raised from the dead and judged, and those found worthy will enter Paradise. At issue is, what do the faithful have to do to advance the end-time?

Predictably, Judaism, at its end of the continuum, asks the faithful to carry out God’s will as stated from the beginning, sanctifying the Sabbath of creation one time in accord with the Torah. So Judaism looks inward, within Israel, for the salvation of humanity through Israel’s own act of sanctification. Then who is saved at the end, if not all those who acknowledge the one true God? And that will encompass, the prophets say, all of humanity.

At the other end of the continuum, Islam holds that no human effort can advance or retard the Last Day. God alone will recall His creation to Himself in His own good time. All human beings can do is prepare themselves for the Day of Resurrection by living daily lives of piety and probity. At the Resurrection all who have died before will be called forth with all who are living to face the accounting of their earthly lives and inherit accordingly either Paradise or the Fire as their eternal abode.

And Christianity takes a middle position, insisting that the world as we know it, down to the very bodies we inhabit, is to be changed definitively. But in that transformation, a metamorphosis from flesh to spirit and death to life, the identities that we have crafted during the course of our lives are to endure. All people, with or without an explicit knowledge of the Son of God, have known his image in their human experience: So from the point of view of the eschaton they have fashioned or have refused to fashion an existence which is commensurate with eternity.

These topics show us similarity and difference: a series of single continua, different positions within each continuum.

The interior logic of monotheism raises for the three religions a common set of questions. But then each religion tells the story in its way, and the respective narratives — in character, components and coherence — shape the distinctive responses spelled out here.

That is how the three religions of one God converge and diverge: They converge in their basic structures, which are more symmetrical than asymmetrical, and they diverge in the way their systems work out the implications of monotheism as monotheism is embodied in the continuing narratives, those of Judaism, then Christianity, finally Islam.

Exploring the Monotheistic Religions of the World
Those who follow a monotheistic religion believe in the existence of a single god. This includes many of the well-known faiths including Christianity, Judaism, and Islam. In contrast, some believe in multiple gods and these are known as polytheistic religions.
The gods of polytheistic religions cover an infinite diversity of personalities and spheres of influence, This is because they are viewed as limited in some way, either having formal areas in which they work or having particular and unique personalities and interests in a similar manner to mortals.
Monotheistic deities, however, tend to much more closely resemble each other. Many monotheists accept that their monotheistic deity is the same deity that is being worshiped by monotheists of different religions.
Commonalities in Monotheism
Monotheistic deities are generally all-encompassing beings precisely because they are viewed as the only deity in existence.
In polytheistic religions, responsibility for reality is parceled out among multiple gods. In a monotheistic religion, there is only one god to take on such responsibility, so it is logical that he or she becomes responsible for everything.
As such, monotheistic deities are generally all-powerful, all-knowing, and ever-present. They are also ultimately incomprehensible because finite mortal minds cannot understand the infinite.
Monotheistic deities tend to be fairly non-anthropomorphic. Many monotheists believe it is impious to attempt to depict their deity in any form.

Judaism

Judaism is the original Abrahamic faith. It posits the existence of a single all-powerful, indivisible god.
Jews address their god by a variety of names, including "God" and YHWH, which is sometimes pronounced Yahweh or Jehovah by non-Jews. However, Jews never utter that name, considering it the unpronounceable name of God.) More »

Christianity

Christianity also believes in a single all-powerful god. Yet, most Christians believe the essence of God is divided into Father, Son, and Holy Spirit. The Son took mortal form in the shape of Jesus, born to a Jewish woman named Mary.
The most common term for the Christian deity is "God." More »

Islam

Muslims hold that their god is also the deity of Jews and Christians. In addition, they recognize the prophets of those religions as prophets of theirs. Like Jews, the Islamic view of god is indivisible. Thus, while they accept Jesus as a prophet, they do not accept him as a god or part of god.
Muslims commonly call their deity Allah, although they sometimes anglicize it to "God." More »

Baha'i Faith

Baha'is believe that God is indivisible. However, he periodically sends down manifestations to communicate his will to humanity. These manifestations possess the knowledge of God and are "as God" to humans, but they are not actually pieces of God. They believe these manifestations have appeared in many religions across the world.
Baha'is commonly refer to their deity as Allah or God. More »

Rastafari Movement

Rastas commonly address their god as Jah, short for the Jewish name YHWH. Rastas follow the Christian belief that Jah has incarnated himself on earth. They accept Jesus as one incarnation but also add Haile Selassie as a second incarnation. More »

Zoroastrianism

The deity of Zoroastrianism is Ahura Mazda. He is indivisible. However, a variety of emanations descends from him, which represent various aspects of him.
Zoroastrianism is not an Abrahamic religion. It developed independently of Abrahamic mythology. More »

Sikhism

Sikhs call their god by a variety of names, but the most common is Waheguru. They accept that a variety of religions follow this deity by different names. Sikhs put more emphasis on the concept of Waheguru being a part of the universe itself, rather than being separate from it. More »

Vodou

Vodouisants accept the existence of a single god called Bondye. Bondye is a single, indivisible god who works his will on earth through spirits known as lwa or loa.
Bondye may also be called Gran Met-la, meaning 'Grand Master." More »
Eckankar
ECKists believe every human soul is a fragment of a single god. Their religious practices center on self-realization and understanding in order to regain awareness of that divine nature of the soul.
In Eckankar, the name God is used with a sacred name of HU to be used by the ECK Master, a living prophet.

Tenrikyo

Tenrikyo teaches that humanity is the metaphorical child of God the Parent, Tenri-O-no-Mikoto. God the Parent desires humanity to live joyous, optimistic, and caring lives. Tenrikyo developed within a polytheistic culture, however, so some older documents give the impression that Tenrikyo is polytheistic. More »


If there is one God then why there are so many religions?
I am a Hindu - More specifically, an aspiring Adwaita Vedantin (If you don't know what it is, it is perfectly ok!)

God is a confusing subject, and mostly considered a matter of faith.

To simply put, Rig Veda, one of the Oldest texts in Hinduism says, 'Ekam Sat - Vipraha Bahuda Vadanti' - Means, Truth is One. The Learned describe it in Many ways.

Hinduism believes in cycle of birth and death (samsara) and a soul is born into the world (not necessarily human) many times and passes through different bodies. Human body is a blessing and should be used to realize what the ultimate truth is.

Since each person does various actions (Karmas) and hence experiences various results over millions of births, every person has infinite state.

These qualities can be broadly described as - Sattwam (thought and meditation oriented), Rajas (action oriented - religious rites) and Tamas oriented (also called the left handed path involving stuff that is generally prohibited)

So, based on the nature of person, Hinduism offers multitude options to choose to worship God. This has led to a popular misconception that Hinduism is polytheistic. It is definitely not. It is repeatedly told in all scriptures God is One. He (or even She!) appears in various forms for the devotees to access.

Before Islamic conquests of North India and Christianity came into India, these various ways of approaching God were actually treated as religions. Now all the systems are together bunched together as Hinduism.

There is no food that can be mandated to every person in the world. It depends on the person's preferences, location etc. Similarly, no one way can be prescribed to worship God. To terrorize ("I'll kill you if you don't worship Y") / blackmail ("If you don't pray to X, you go to Hell, however good person you might be") people into one way of worship doesn't count

To summarize, "Since each human is of infinite state, there needs to be various ways of worshipping God(dess) - All this should lead to One God(dess)"

PS:-
Hinduism as it is now, is a bunch of philosophies which includes (conflicting) options like 'No God' (Sankhya by Sri Kapila), God exists but different from the individual soul ('Dwaita'), God exists, but is sum of all individual souls (Visishtadwaita), God and individual soul are one i.e. God Alone Exists (Adwaita), God exists, but is not as important as Logic (Nyaya / Vaishseshika by Sri Gautama), God exists and we need to /Unite with Him (Yoga by Sri Patanjali), Karma / Action is Supreme (Mimamsa by Jaimini) etc.

Of all, Adwaita Vedanta which asserts there is no creation at all and all that we perceive is only a relative reality (like that of a dream) and God alone is absolute reality beyond measure of Space and Time, and He alone exists is the closest thing humanity can come close to a Grand Unification Theory searched by the scientists of the yore and current. This is theory is the most beautiful I have seen EVER and doesn't want you to move away from your current faith too!