Monotheism, belief in one God alone, is the conviction the Abrahamic religions share. Judaism, Mandaeism, Christianity and Islam each confess one God. Yet they express that belief in different ways, and the differences have shaped centuries of debate. Each tradition has also had to explain how the one God relates to the world He made, to the revelation He sent, and to the prophets and messengers who carried it.
In this article
Judaism: the Shema
The central declaration of Jewish faith begins, “Hear, O Israel: the Lord is our God, the Lord is one.” Recited morning and evening, the Shema affirms that God is one and unique. The medieval philosopher Maimonides counted belief in God’s absolute unity among the foundational principles of Judaism and taught that God has no body and no likeness.
Christianity: the Trinity
Christians also affirm one God, but understand that one God as existing eternally in three persons: Father, Son and Holy Spirit. The doctrine took formal shape at the councils of Nicaea in 325 and Constantinople in 381, as the church sought to account for its worship of Jesus as divine without abandoning monotheism. Christian theologians insist that the three persons share one divine nature and are not three gods.
Islam: tawḥīd
Islamic theology is built on tawḥīd (توحيد, oneness), the absolute unity of God. The Qur’an declares that God is one, eternal, neither begetting nor begotten, and without equal. Its opposite is shirk (شرك, association), ascribing partners to God, which Islam regards as the gravest sin. Muslim theologians developed detailed discussions of God’s names and attributes and of how they relate to God’s unity.
Mandaeism: the Great Life
Mandaeans call God Hayyi Rabbi, the Great Life, the source of the World of Light. Below it lies a World of Darkness, and the created world stands between the two. The human soul belongs to the light and is exiled in the body; it returns to its source through nāṣerutā, the knowledge carried by the rites and the priesthood. Mandaean monotheism is therefore joined to a dualism of light and darkness that the other three traditions reject. See Mandaeism.
Points of disagreement
Jewish and Muslim thinkers have historically questioned whether the doctrine of the Trinity is compatible with strict monotheism. Christian thinkers have answered that the Trinity describes the inner life of the one God and does not divide it. Muslims and Christians also differ over the identity of Jesus: Christianity confesses him as the incarnate Son of God, while Islam honours him as a prophet and a servant of God.
Common ground
The traditions agree that God is the sole creator, is just and merciful, speaks to humanity through prophets, and will judge the world. Much interfaith conversation starts from these shared affirmations while taking the differences seriously.
Judaism and Islam state the principle in its least qualified form: one God, without partner or likeness. The Qur’an adds a claim of its own, presenting that confession as the faith of Abraham himself, which is why Muslims describe their religion as the restoration of the monotheism from which the whole family takes its name. See The path of Abraham in the Qur’an.
More on monotheism
Further reading: Prayer across the Abrahamic traditions and Faith and reason in medieval Jewish, Christian and Muslim thought, Al-Ghazali, Ibn Rushd and the limits of reason, Monotheism (Encyclopaedia Britannica).
