Adoptionism is a heretical theology that claims Jesus was God’s adopted Son. Adoptionism teaches that, because of Jesus’ sinless life, God chose Him and adopted Him. Adoptionism also goes by the name dynamic monarchianism; it was declared a heresy by the church in the second century. Scripture makes it clear that adoptionism is not true. Jesus Christ is not adopted; He is “begotten” (John 3:16, KJV).
Adoptionism claims that, before His adoption, Jesus was a mere man, although sinless. However, we know, biblically, that all men are under the curse of Adam and there are no sinless men (Romans 5:12–14). Further, no man can be justified by the works of the Law (Romans 3:19–20). Jesus was sinless (2 Corinthians 5:20–21), but that was because He was not just a man; He was fully God, as well (John 1:1, 14). The pre-existence of Christ, the titles applied to Jesus, and the worship He received all bear witness of the divine nature of the Lord.
Adoptionism is disproved in the first few words of John’s gospel. John equates Jesus with “the Word of God” and says Jesus was “in the beginning with God.” In fact, “all things were made through him,” and “in him was life and the life was the light of men” (John 1:1–5). These are not statements one makes about a sinless man adopted by God. Furthermore, John points out that John the Baptist was sent to bear witness to the light (verse 14). If Jesus were simply a good man whose good deeds caught God’s attention and earned God’s love, the role of John the Baptist would be pointless. Prophecies in the Old Testament that anticipate Jesus’ virgin birth (Isaiah 7:14), crucifixion (Psalm 22), and atoning sacrifice (Isaiah 53:5, 12) would not make any sense if God simply “noticed” that Jesus was sinless and adopted Him after the fact.
Lastly, John says, “The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the one and only Son, who came from the Father, full of grace and truth” (John 1:14). The phrase “one and only Son” is translated as “only begotten Son” in some other translations. The idea is that Jesus is the only one of His kind: He is uniquely God’s Son, the only One who shares the same divine nature as God. The Word “became flesh,” so He obviously had an existence before becoming human. Jesus was God’s only Son before He came to earth. Believers have been adopted into God’s family (Ephesians 1:5), but Jesus was always God’s unique Son.