Concept

Monotheism

Intro

"Hear, O Israel, the LORD our God, the LORD is one."

That sentence, the Shema, is the heart of monotheism. Monotheism is the teaching that exactly one God exists, one uncreated being who is the source of everything else. It is what Israel confessed in the Old Testament, what historic Christianity confesses, and what Islam confesses.

Within the monotheist family there are three live forms.

Strict unitarian monotheism says God is one Person, period. This is the position of Judaism and Islam.

Trinitarian monotheism says God is one being who exists eternally as three Persons (Father, Son, and Holy Spirit) who share one undivided divine nature. This is the historic Christian position. It is not tritheism (three gods) and not polytheism with a head god on top. It says one God exists in three eternal personal relations.

Modalist monotheism says God is one Person who plays three roles in different times or settings, like an actor changing costumes. The mainstream of all three Abrahamic religions rejects this.

The Jewish and Muslim objection to Christianity is that the Trinity is sneaking polytheism in through the back door. The Christian reply is that Trinitarian monotheism is genuine monotheism. There is one being, one divine substance, one will, one set of attributes. The threeness is the threeness of personal relations within that one being, not three separate gods.

The page covers the Old Testament data first, starting with the Shema, moving through the first commandment and the major Isaiah monotheism passages (Isaiah 44:6, 45:5, 45:21). Then it covers the New Testament, where the Christian writers do not drop monotheism but rewrite the Shema around Jesus, as Paul does in 1 Corinthians 8:6 when he splits the Lord is one clause between the Father (called theos) and the Son (called kyrios). It walks through the philosophical case for one God instead of many. It covers the patristic and conciliar development. And it covers the modern conversations about how to keep monotheism without collapsing into modalism or expanding into tritheism.

For the dedicated argument against Oneness theology, see Trinity vs Oneness vs Modalism vs Arianism. For the case that Israel's monotheism was original and not a later development, see Israelite Monotheism.

In full

Monotheism is the doctrine that there is exactly one God, one being who is the uncreated, self-existent source of everything else. It is the foundational confession of Israel, of historic Christianity, and of Islam. Within monotheism three forms are theologically live: strict unitarian monotheism (Jewish, Islamic), Trinitarian monotheism (Christian), and modalist monotheism (rejected by all three mainstream traditions). The Christian claim is that Trinitarian monotheism is genuine monotheism, one God in three persons, and not a disguised polytheism or tritheism.

OT anchor, the Shema and the Isaianic monotheism

The OT teaches monotheism not as an inference but as a covenant confession.

Deuteronomy 6.4, the Shema. "Hear, O Israel, the LORD our God, the LORD is one" (NASB95). The Hebrew YHWH eloheinu YHWH echad admits two readings: (a) YHWH is unique (the only God), or (b) YHWH is one (numerically singular). Both are exegetically defensible; classical Jewish reading takes (b) as primary, Christian reading often takes (a) as primary and (b) as compatible with internal triunity. The word echad itself is famously a unity-permitting number, used of a compound unity in Gen 2:24 ("they shall be one flesh") and elsewhere, though this argument is over-leaned-on by some Christian apologists; the lexical point doesn't establish the Trinity, it only blocks one Jewish objection.
Exodus 20.3, the first commandment. "You shall have no other gods before Me." A relational-exclusivity claim with metaphysical entailment: the LORD will not share covenant loyalty.
Isaiah 44.6; Isaiah 44.8; Isaiah 45.5; Isaiah 45.21; Isaiah 46. The Isaianic monotheism is the OT's most explicit. "I am the first and the last, and there is no God besides Me" (Isa 44:6); "There is no other God besides Me, a righteous God and a Savior; there is none except Me" (Isa 45:21). These passages move beyond henotheism (worship one but acknowledge others) to ontological exclusivism: the other "gods" are nothing (Isa 44:9-20 on idols).
Other anchors. 1 Kings 8:60 ("there is no one else"); Jer 10:1-16 (idol satire); Neh 9:6 ("You alone are the LORD").

NT monotheism

The NT does not retreat from OT monotheism, it intensifies it while restructuring it Christologically. Paul, a Pharisee Jew, retains the Shema and rewrites it around Jesus:

"Yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him." (1 Cor 8:6, NASB95)

Richard Bauckham's central argument (God Crucified; Jesus and the God of Israel) is that Paul has split the Shema across Father and Son without lapsing into polytheism, including Jesus inside the unique divine identity. See Richard Bauckham.

Other NT monotheistic confessions:

"There is no God but one" (1 Cor 8:4).
"For there is one God, and one mediator also between God and men, the man Christ Jesus" (1 Tim 2:5).
"You believe that God is one. You do well; the demons also believe, and shudder" (Jas 2:19).
"One God and Father of all who is over all and through all and in all" (Ephesians 4.6).

The three forms of monotheism

1. Strict unitarian monotheism

God is one person. The divine essence is not internally distinct from the divine person; "God" names one numerically single self.

Judaism, post-Temple rabbinic Judaism and most contemporary Jewish theology hold strict unitarian monotheism. Maimonides's Thirteen Principles anchor it: "The Creator, blessed be His Name, is a Unity, and there is no unity in any manner like Him." See Maimonides.
Islam, tawhid is the indivisible oneness of Allah; shirk (associating partners with Allah) is the unforgivable sin. The Qur'an's polemic against Christianity ("Say not 'Three', desist!", Surah 4:171) is the most sustained ancient critique of Trinitarianism. See Tawhid.
Modern unitarian Christianity, Socinians, 19th-century Unitarians, and contemporary Biblical Unitarians (e.g., the Christadelphian tradition) reject the Trinity while retaining Christian Scripture. Jehovah's Witnesses reject the Trinity but are not classical unitarians, they hold a modified Arianism in which Jesus is the first-created angelic Logos.

2. Trinitarian monotheism, the Christian form

God is one being (essence, ousia) existing eternally in three persons (hypostases): Father, Son, and Holy Spirit. The persons are not three Gods, three parts of God, or three modes of God, they are three subsisting relations in the one indivisible divine essence, distinguished only by relations of origin (paternity, filiation, spiration).

The classical formula (Cappadocian / Augustinian / Thomist):

One ousia (one in essence, nature, will, power, glory). The Father, Son, and Spirit do not divide the divine being; each is wholly God. This safeguards monotheism.
Three hypostases (three subsisting persons). The Father is not the Son, the Son is not the Spirit, the Spirit is not the Father. This safeguards distinction.
Distinguished only by relations of origin, the Father is unbegotten (source of deity); the Son is eternally begotten of the Father; the Spirit proceeds from the Father (and, in the Western tradition, the Son, see Filioque). The persons do not differ in attributes, only in their internal relations.

See Trinity for full treatment; Trinity vs Oneness vs Modalism vs Arianism for the comparative spread; Trinity Coherence Defense (Latin-Thomist) for the analytic case that the doctrine is coherent.

3. Modalist monotheism, rejected

God is one person playing three roles or wearing three masks. The Father, Son, and Spirit are not three distinct subjects but three modes of one person, sometimes one at a time (sequential modalism / Sabellianism), sometimes as three faces of the same self (modal monarchianism).

See Modalism. Held today primarily by Oneness Pentecostalism (United Pentecostal Church International). Rejected by all branches of historic Trinitarian Christianity because it cannot make sense of the simultaneous distinctions in the NT (Father speaks while Son is baptized while Spirit descends; Son prays to the Father; Son asks the Father to send the Spirit).

"Christianity is polytheism", the charge

The polytheism charge against Trinitarianism comes most forcefully from Islamic apologetics and from Jehovah's Witnesses, with secondary echoes in rabbinic anti-Christian polemics.

The Islamic version

The Qur'an addresses what it takes Christians to say: "They have certainly disbelieved who say, 'Allah is the third of three.' And there is no god except one God" (5:73); "Do not say 'three'" (4:171). The objection treats the Trinity as either:

Three Gods stacked together (tritheism), or
A composite God with parts (incompatible with simplicity).

Response. Neither is what Trinitarian Christianity teaches. The Trinity is not three Gods because there is one ousia, one divine being, one will, one power, one glory. It is not composite because the persons are not parts of the essence; each person is wholly God, identified with the whole divine essence under different relational modes. Divine simplicity (Divine Simplicity) explicitly rules out composition.

The Islamic objection often relies on the Qur'an's apparent misidentification of the "third" of the Trinity, Surah 5:116 presents Mary as the third member, implying the Qur'an polemicizes against a heretical Marian devotion rather than orthodox Trinitarian doctrine. Either way, the standard tawhid objection conflates numerical persons with numerical Gods; it equivocates between the count of self-subsisting beings (one) and the count of subsisting personal relations within that being (three).

See Tawhid, Islamic Dilemma.

The Jehovah's Witness version

The Watchtower argument is exegetical rather than philosophical: the NT never explicitly says "Trinity"; Jesus calls the Father "the only true God" (John 17:3); Jesus prays to the Father (suggesting non-identity); the Spirit is presented impersonally; therefore Trinitarianism is post-biblical importation.

Response. None of these conclusions follow.

Trinity as a term is post-biblical; the doctrine is biblical, it is the only synthesis that holds together (i) strict monotheism, (ii) deity of the Son (Christs Deity; John 1:1; 20:28; Col 2:9; Heb 1:8-12), and (iii) deity of the Spirit (Pneumatology; Acts 5.3-4).
"The only true God" in John 17:3 is set against false gods, not against the Son. The same Gospel calls Jesus theos (1:1) and has Thomas confess him as "my Lord and my God" (20:28).
Praying to the Father is what we expect on Trinitarianism, the Son has a distinct relational mode and submits to the Father in the economy without ceasing to be of one essence with him.
The Spirit's personhood is exegetically demonstrated; see Pneumatology.

The rabbinic version

Some Jewish polemics treat shituf, "association," roughly the inclusion of any second hypostasis in the divine identity, as a step into polytheism. Maimonides's principles formalize this. Pre-rabbinic Judaism, however, was not as monolithic as later orthodoxy: figures like Philo and texts like the early Logos traditions of Second-Temple Judaism allowed for "second power in heaven" speculation (Alan Segal's research), which Christian theology took up and Christianized. The Christian claim is that Trinitarian distinctions are not foreign imports but the actualization of latent OT theology, the malak YHWH / Angel of the LORD theophanies, the Wisdom literature, the personification of Word and Spirit.

See Angel of the LORD, Philo of Alexandria.

Why Trinitarian monotheism is genuine monotheism

The metaphysical claim, compressed:

Polytheism is the existence of multiple self-subsisting divine beings (multiple instances of the divine kind).
Trinitarianism posits one self-subsisting divine being in which there are three subsisting personal relations.
Counting beings (one) is not the same operation as counting persons-within-a-being (three); they are different counts of different kinds of things.
Therefore Trinitarianism asserts strict numerical-being monotheism while allowing internal personal distinction, and is not polytheism.

The remaining objection, that person on the Trinitarian use is not really the same as person on the human use, is not a polytheism objection but a coherence objection. It is answered by clarifying that "person" in Trinitarian theology is a technical term for a subsisting relation, not a Cartesian self. See Trinity Coherence Defense (Latin-Thomist).