“Trinity” means “three-in-one.” It’s true, the word “Trinity” is not in the Bible. But the concept is.
The true religion has always stated that there is only one Divine Essence who is called “God.” From the beginning of time God has revealed himself as the LORD God (Genesis 2:4) and there is no other but him (Isaiah 44:6). Monotheism set the Hebrews apart from other nations (Deuteronomy 6:4), and Christianity follows the same truth.
God the Father is God. Jesus spoke of him as “the only true God” (John 17:1,3). The apostle Paul spoke of God the Father as the creator God and the source of life (1 Corinthians 8:6).
God the Son is God. Hebrews chapter one emphasizes that fact, explicitly saying “the Son is the radiance of God’s glory and the exact representation of his being, sustaining all things by his powerful word” (1:3). We believe as the Bible teaches that “in Christ all the fullness of the deity dwells in bodily form” (Colossians 2:9). And we believe that “he is the true God and eternal life” (1 John 5:20). Besides, the Bible attributes to Jesus all the characteristics of God (Matthew 28:18). Jesus is also to be worshiped as true God (Matthew 28:17; Hebrews 1:6). The New Testament shows that Jesus is the redeemer of the world from sin and the power of Satan.
God the Holy Spirit is God. “The Lord is the Spirit, and where the Spirit of the Lord is, there is freedom” (2 Corinthians 3:17). He is distinguished from the Father and Son when Jesus said, “I will ask the Father, and he will give you another Counselor, the Spirit of truth, to be with you forever” (John 14:16-17). The Holy Spirit is more than an impersonal power of God. He grieves (Ephesians 4:30), and is the person of the Trinity who works faith in our hearts. Ananias lied to the Holy Spirit (Acts 5:3). Some people “speak against the Holy Spirit” to their damnation (Matthew 12:32).
There are many places in Scripture that mention all three Persons of the Triune God (Matthew 4:16-17). God has always presented himself in plural terms (Genesis 1:26).
There are three Persons, each one the complete God, and yet there is no more than one single God. “We worship one God in three persons and three persons in one God” (from the Athanasian Creed of the Christian church).
The Father is God. The Son is God. The Holy Spirit is God. And they are one God.