Is There Only One God? Monotheism in Judaism, Christianity, and Islam

Judaism is perhaps the oldest and most uncompromising voice for monotheism in human history. The foundational declaration of Jewish faith, the Shema, states plainly:

Hear, O Israel: The LORD our God is one LORD. (Deuteronomy 6:4)

The Torah reinforces this in multiple places. Deuteronomy 4:35 declares:

Unto thee it was shewed, that thou mightest know that the LORD he is God; there is none else beside him.

Know therefore this day, and consider it in thine heart, that the LORD he is God in heaven above, and upon the earth beneath: there is none else.

The first of the Ten Commandments reinforces this exclusivity:

Thou shalt have none other gods before me.

Among the gods there is none like unto thee, O Lord

Rabbinic tradition developed the concept of yichud Hashem (the unification of God's name) as a devotional act. Modern Jewish thinker Hermann Cohen (d. 1918) argued that Jewish monotheism was the very engine of ethical universalism. There's no serious internal debate in Judaism about whether God is one — that's settled. The debates concern what divine unity entails.

Christianity inherits the Jewish confession of one God entirely — but complicates it through the doctrine of the Trinity. Paul writes in 1 Corinthians 8:6:

But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him.

there be that are called gods, whether in heaven or in earth, (as there be gods many, and lords many,)

Christianity affirms the Old Testament witness without reservation. Deuteronomy 6:4 is quoted by Jesus himself in the Synoptic Gospels as the greatest commandment, and the prohibition

Thou shalt have no other gods before me

The complication, of course, is Trinitarian theology. The Council of Nicaea (325 CE) formalized the belief that Father, Son, and Holy Spirit are three distinct persons sharing one divine substance (homoousios). Theologian Karl Barth (20th century) described this as God's self-revelation in three modes, not three separate gods. Critics — including Jews and Muslims — have long argued this amounts to a form of polytheism, a charge Christian theologians like Augustine (354–430 CE) and Thomas Aquinas (1225–1274 CE) spent considerable effort refuting.

It's worth noting there's genuine disagreement within Christianity itself. Unitarians, for instance, reject the Trinity and hold a strictly unitary monotheism much closer to the Jewish model. But mainstream Catholic, Orthodox, and Protestant traditions all insist: one God, three persons — not three gods.

Not applicable in terms of the retrieved scriptural passages, which are drawn from the Hebrew Bible and New Testament. However, the question of God's oneness is absolutely central to Islam and cannot be omitted from this comparison.

Islam's answer to 'Is there only one God?' is the most emphatic and theologically precise of the three traditions. The concept of tawhid — the absolute oneness and indivisibility of God (Allah) — is the foundational pillar of Islamic belief. The Islamic declaration of faith, the Shahada, begins: 'There is no god but God' (La ilaha illa Allah). Surah Al-Ikhlas (112:1–4) is considered by Islamic scholars to encapsulate the entire theology of divine unity in four verses: 'Say: He is Allah, the One; Allah, the Eternal Refuge; He neither begets nor is born; nor is there to Him any equivalent.'

Islamic theology explicitly rejects the Christian Trinity as shirk (associating partners with God), which is considered the gravest possible sin in Islam. The Qur'an directly addresses this in Surah An-Nisa (4:171), urging Christians not to say 'Three.' Scholar Ibn Taymiyya (1263–1328 CE) wrote extensively on tawhid, distinguishing between the oneness of God's lordship (tawhid al-rububiyya), the oneness of His names and attributes (tawhid al-asma wa'l-sifat), and the oneness of worship (tawhid al-uluhiyya).

Islam also affirms the original monotheism of the Hebrew prophets and sees itself as restoring the pure, uncompromised monotheism that Judaism and Christianity have — in the Islamic view — either preserved or distorted respectively.

Judaism answers yes: God is one. The Shema states, “Hear, O Israel: The LORD our God is one LORD,” which functions as Israel’s core confession of divine unity. Deuteronomy 6:4 The covenant prohibits other deities: “Thou shalt have none other gods before me.” Deuteronomy 5:7 Israel is reminded, “the LORD he is God; there is none else beside him,” and to fix this on their heart: “the LORD he is God in heaven above, and upon the earth beneath: there is none else.” Deuteronomy 4:35 Deuteronomy 4:39 Even when other powers are mentioned, the LORD’s absolute supremacy is affirmed: “For the LORD your God is God of gods, and Lord of lords,” and “Among the gods there is none like unto thee, O Lord.” Deuteronomy 10:17 Psalms 86:8

Christianity also says yes, there is one God. Paul writes, “to us there is but one God, the Father… and one Lord Jesus Christ,” explicitly contrasting the many so‑called “gods” and “lords” referenced in surrounding cultures. 1 Corinthians 8:6 1 Corinthians 8:5 This Christian confession is read in continuity with Israel’s Shema (“The LORD our God is one LORD”), aiming to uphold monotheism while confessing Jesus as Lord. Deuteronomy 6:4 Christians debate how best to relate these verses, but the shared claim is that God is one. 1 Corinthians 8:6 Deuteronomy 6:4

Not applicable. Concerns Islamic scripture/practice; no direct counterpart can be provided from the retrieved passages for proper citation.