The Word becoming flesh means that the eternal Son of God took upon himself a true human nature—body and soul. This taking on of a human nature is also attested elsewhere in Scripture (Romans 1:3; Romans 8:3; Galatians 4:4; Philippians 2:7; 1 Timothy 3:16; Hebrews 2:14). When the Word became flesh, he did not cease to be God; he remains the true and eternal God. However, now the Son has both a divine and a human nature. Thus, the incarnation is not the coming into existence of the Son, but rather the moment in which the Son became a human being in addition to being a divine being.1
The true human nature of Jesus is taught throughout John’s Gospel (John 4:6–7; John 6:53; John 8:40; John 11:33, John 11:35; John 12:27; John 13:21; John 19:28) but the relation of the two natures to one another will forever remain a mystery, far above our comprehension. The incarnation is not for us to understand but believe.2
14 And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.