The word Trinity is not used in the Bible, but the doctrine of the tri-unity of God is clearly taught in the New Testament. The Old Testament does not explicitly teach the doctrine, but the concept of the Trinity is hinted at in certain places. We could say that the Old Testament lays a foundation for the later revelation concerning the Trinity.
The doctrine of the Trinity finds support in the Old Testament in the Hebrew concept of plurality in unity:
Deuteronomy 6:4 is a verse that seems, at first, to wholly negate the doctrine of the Trinity: “Hear, O Israel: The LORD our God, the LORD is one.” (Interestingly, the singular Yahweh is coupled with the plural Elohim in this verse.) The word translated “one” is ehad, which means “one” or “unity”; however, the word is also used in other contexts to suggest a plurality within unity. For example, the word ehad also appears in Genesis 2:24, which considers two persons as one: “[A man] is joined to his wife, and the two are united into one [ehad]” (NLT). Obviously, the husband and wife are distinct persons, but they are called “one”—there is diversity within the unity.
The doctrine of the Trinity finds support in the Old Testament in the names for God:
The very fact that God reveals Himself using multiple names in the Old Testament could be a clue pointing to His triune nature. Two of the names show up right away: Elohim in Genesis 1:1, and Yahweh in Genesis 2:4. Some scholars believe the multiple names for God imply a diversity within the Godhead.
One of the Hebrew names for “God” in our Bible, Elohim, is plural in form. The -im suffix is plural, and elohim, when not referring to the One True God, is translated as “gods” (plural) in Scripture. The plural form of a name for the One God could be seen as implying a perfect unity of Persons and is certainly consistent with the New Testament teaching of the Trinity.
Adonai, translated in our Bibles as “Lord,” occurs about 300 times in the Old Testament. This title for God is also plural. One writer comments on the word Adonai, “It is significant that it is almost always in the plural and possessive, meaning ‘my Lords.’ It confirms the idea of a trinity as found also in the name of Elohim” (Stone, Nathan, The Names of God, Moody Publishers, 2010, p. 35).
The doctrine of the Trinity finds support in the Old Testament in the appearances of the Angel of the Lord:
In several places, the Old Testament records encounters with someone called “the Angel of the Lord.” This supernatural presence speaks as if He is God, identifies Himself with God, and exercises the responsibilities of God. For example, in Genesis 16:10, the Angel of the Lord says to Hagar, “I will increase your descendants so much that they will be too numerous to count.” Of course, God is the One who blesses Ishmael, but it’s the Angel of the Lord who personally makes the promise to his mother.
The same Angel of the Lord appears to Abraham and assumes the role of God, saying, “Now I know that you fear God, because you have not withheld from me your son, your only son” (Genesis 22:12, emphasis added ). See also Exodus 3:2; Judges 2:1–4; 5:23; 6:11–24; 13:3–22; 2 Samuel 24:16; Zechariah 1:12; 3:1; 12:8. In several passages, those who see the Angel of the Lord fear for their lives because they had “seen the Lord.” It’s clear that the Angel of the Lord was no mere angel. Viewed through the lens of the New Testament teaching of the Trinity, it’s easy to conclude that the Angel of the Lord could be a pre-incarnate appearance of Christ.
The doctrine of the Trinity finds support in the Old Testament in its descriptions of the Spirit of God:
The post-exilic Levites speak of the Spirit of God as being sent by God and speaking for God: “You also gave Your good Spirit to instruct them” (Nehemiah 9:20, NKJV); and “For many years you were patient with them. By your Spirit you warned them through your prophets” (Nehemiah 9:30). Both verses seem to make a distinction between God and another personality called the Spirit of God. See also Isaiah 48:16 and Isaiah 63:10.
The doctrine of the Trinity finds support in the Old Testament in God’s self-references:
Most of the time, God speaks of Himself using singular pronouns (e.g., Exodus 33:19; Hosea 11:9); at other times, He uses plural pronouns:
“Then God said, ‘Let us make mankind in our image, in our likeness’” (Genesis 1:26, emphasis added).
“And the LORD God said, ‘The man has now become like one of us, knowing good and evil’” (Genesis 3:22, emphasis added).
As sinful humanity was erecting the tower of Babel, God said, “Come, let Us go down and confuse their language” (Genesis 11:7, BSB, emphasis added).
In Isaiah 6:8, God refers to Himself in both singular and plural terms: “Then I heard the voice of the Lord saying, ‘Whom shall I send? And who will go for us?’” (emphasis added).
We could assume that, in each of the above passages, God is simply using the majestic plural to emphasize His power and greatness. Or we could also assume that there’s something more going on—viz., that these statements hint at discrete personalities existing as a unified whole.
The doctrine of the Trinity finds support in the Old Testament in Messianic passages:
In Psalm 110:1, David writes, “The LORD said to my Lord, ‘Sit at My right hand, Till I make Your enemies Your footstool’” (NKJV). Here is an example of Yahweh speaking to Adonai and giving Him the place of highest honor in heaven. Jesus pointed to this psalm as proof that the Christ is more than David’s descendant—He is the pre-existent Lord and much greater than David (Matthew 22:41–45).
Another Messianic prophecy is found in Psalm 45:6–7: “Your throne, O God, will last for ever and ever; a scepter of justice will be the scepter of your kingdom. You love righteousness and hate wickedness; therefore God, your God, has set you above your companions by anointing you with the oil of joy.” The psalmist, addressing Elohim, suddenly speaks of “your God” who honors and anoints the Addressee.
The doctrine of the Trinity finds support in the Old Testament in the repetition of God’s qualities or His name:
In Isaiah 6:3, the angels surrounding God praise Him as being “holy, holy, holy.” The threefold repetition expresses the intensity and completeness of God’s holiness. Some scholars also infer from the angels’ words an expression of the triune nature of God, as the three Persons of the Godhead are each equal in holiness and majesty.
Similarly, we have a threefold repetition of God’s name in Numbers 6:24–26:
“The Lord bless you
and keep you;
the Lord make his face shine on you
and be gracious to you;
the Lord turn his face toward you
and give you peace.”
The blessing’s appeal to “the Lord . . . the Lord . . . the Lord” is seen by some scholars as providing a glimpse of the Trinity.
In many ways, the Old Testament gives a preview of the New Testament’s fuller revelation, including the doctrine of God as a triune Being. While the Trinity is not clearly seen in the Old Testament, there are certainly indicators of that truth.