The word Trinity is not used in the Bible. But is there any similar support for the doctrine of Trinity in the Old Testament?
The Christian doctrine of the Trinity is the heart of all revelation given to man. Although the word itself is never used in Scripture, anyone who reads the Scripture seriously will find it to be an inescapable concept. The word Trinity which means "tri-unity" or "three-in-oneness" best expresses the mystery of God ??? One God who eternally exists as three Persons.
The doctrine of the Trinity is a progressive revelation ??? the Old Testament gives fragmentary but definite hints about it, whereas the New Testament gives a fuller and more explicit presentation of the concept.
1. The angel of the Lord: Throughout the Old Testament we see a noteworthy figure called "the angel of the Lord" who sometimes speaks as if he were God himself, and at other times appears to be an envoy sent by the Lord. In Genesis 16:10, 13: "The angel of the Lord also said to her, 'I will surely multiply your offspring so that they cannot be numbered for multitude'??? So she called the name of the Lord who spoke to her, 'You are a God of seeing.'" In Genesis 22:11-12, the angel of the Lord speaks from heaven as if He is the same God who commanded Abraham. In Judges 2:1-2, the angel of the Lord says, "I brought you up from Egypt and brought you into the land that I swore to give to your fathers." In light of the New Testament revelation, many recognize the angel of the Lord to be a pre-incarnate appearance of Christ (Christophany) who has been active in salvation and judgment throughout Israel's history.
2. Distinction of Persons: Psalm 45:6-7 addresses the king as "God" and then says to the person called "God," that "God, your God has anointed you with the oil of gladness beyond your companions." The writer to the Hebrews quotes this passage and applies it to the Lord Jesus Christ (Hebrews 1:8). Psalm 110:1 records, "The Lord says to my Lord: 'Sit at my right hand, until I make your enemies your footstool.'" Jesus himself pointed out to the Pharisees that David was calling two separate persons as "Lord" (Matthew 22:41???46). Who could sit at the right hand of God unless he is someone equal to God?
3. The Spirit of God: In the Old Testament, the Spirit of God is both distinguished from and identified with God. Psalm 51:11 distinguishes between God's "presence" and "Your Holy Spirit." Isaiah 63:10 says the Holy Spirit can be "grieved." Isaiah 48:16 speaks of "the Lord God" who "has sent me, and his Spirit" ??? three persons in one verse.
Passages like these, from the Old Testament, could be multiplied to make a case that there is a definite indication of plurality of persons in one God. Suffice it to say, the readers of the Old Testament do not have to strain their eyes to see glimpses of the Trinity.