The term trinity is from the Latin trinitas, which means “three.” The Bible was originally written in Hebrew (most of the Old Testament), Aramaic (small portions of the Old Testament), and Greek (the New Testament), and so the term trinitas is not found anywhere in the Bible. The term trinity was used to describe the triunity (or three-ness) of God, as described in Scripture. While the term is not used in the Bible and is a later theological descriptor, trinity is an appropriate and helpful term to describe the unity and plurality of the Persons of God.
From the very first words of the Bible, it is evident that there is plurality with God. Even the Hebrew word used for God (Elohim) in Genesis 1 and throughout much of the Hebrew Scriptures (or Old Testament) is in the plural form. God is distinguished from the Spirit of God (Ruach Elohim) in Genesis 1:1 –2. Then, Genesis 2:4 adds a further distinction in identifying the Lord God (Yahweh Elohim) as the Creator. Throughout biblical history, the Lord (Yahweh) God is identified as the Person who would interact—often in physical form—with humanity (e.g., Genesis 3:8; 12:1). This One is often referred to as “the angel of the Lord” (Genesis 16:7–11, 22:11–15; Exodus 3:2, 4, etc.) and even sometimes as “a man” (Genesis 32:24–30). It is clear from these early references that there are three distinct Persons who are one in essence and equality: God, the Spirit of God, and the Representative of God to humanity. Of course, the term representative is not used in these contexts, but it seems an appropriate term to illustrate the role of this particular Person. Regardless of the terms preferred, God is described as being three Persons. This is what the term trinity conveys.
Perhaps due to the perceived complexity of the concept that God is one God and yet three Persons, there have developed two alternative explanations for the plurality attributed to God. One suggests that the three-ness of God really means three totally separate gods (a polytheistic view of the Trinity), while another argues that the three-ness or trinity is really just referring to three expressions or modes of the same person (a modalistic view of the Trinity). While these two approaches try to bring clarity to what is often thought to be a difficult idea, the biblical text is clear on how we should understand the Trinity, and neither modalism nor polytheism are compatible with what the Bible teaches. This plurality and singularity are such important aspects of who God is that God identifies Himself to the Israelites in this way: “Hear, O Israel, Yahweh is our Elohim. Yahweh is one” (Deuteronomy 6:4).
God directly asserts His triunity in Isaiah 48. The One who named (or called) Israel is speaking in Isaiah 48:12. The renaming of Jacob to Israel occurred in Genesis 32:28 when the “man” Jacob was wrestling gave Jacob a blessing. Jacob recognized that man as God (Genesis 32:30). This same One refers to Himself as “the first and the last” and had earlier identified Himself as Yahweh, the King of Israel, the first and the last, and the only God (Isaiah 44:6). This One claims to be the Creator (Isaiah 48:13). He also importantly adds that “now the Sovereign Lord has sent me, endowed with his Spirit” (Isaiah 48:16). So, God is sent by the Lord God (Adon Yahweh) and by His Spirit.
All of the things said in Isaiah 48 are applied to Jesus in the New Testament. He is the Yahweh who interacted with Abraham (John 8:56–59). He was born to be the King of Israel (Matthew 2:2). He is the first and the last (Revelation 1:17; 2:3; 22:13). He is the Creator (John 1:3). He was sent by His Father and empowered by the Spirit (Matthew 3:16–17; John 1:32–34, 5:23). In Isaiah 48:12 and 16, the preincarnate Jesus identifies Himself as God yet distinguishes Himself from the One He refers to as His Father and from the Spirit, just as He distinguishes the three again in John 14:15–16 and in Matthew 28:19.
The triunity of God as one God and three Persons, known as the Trinity, is a central biblical teaching and a central point of the teaching of Jesus Himself.