Jesus is God in human flesh, he has two natures (one human, one divine), yet he is one person. In the incarnation, God came to earth in the person of Jesus Christ to save us from our sins. The Word became flesh is therefore, the very heart of Christianity.
At the very heart of the Christian faith we find the doctrine of the incarnation–Jesus Christ, the second person of the Holy Trinity, and the eternal son of God, took to himself a true human nature in the womb of the virgin for the purpose of saving us from our sins.
The incarnation of Jesus marks Christianity off as a thoroughly supernatural religion, grounded in a specific truth claim–i.e., God was in Christ reconciling the world to himself (cf. 2 Corinthians 5:18). The incarnation aims not for the moral improvement, enlightenment, or personal benefit for the followers of Jesus, but accomplishes the salvation of all those sinners whom God has chosen to save in Jesus Christ. Jesus is not merely our example, but primarily our Savior.
The incarnation of Jesus Christ is also the proof that God keeps his promises. This remarkable historical event is the key turning point in what is truly the greatest story ever told. At the dawn of human history, God placed Adam in Eden and commanded him not to eat from the tree of the knowledge of good and evil. But Adam ate from the forbidden tree, plunging the entire human race into sin and death. But even as God was pronouncing the curse upon Adam, Eve, and the serpent (as recounted in Genesis 3), God promised to rescue Adam from the consequences of his act of rebellion through the seed of the woman–that is, through a biological descendant from Eve who will redeem God’s people from their sin (Genesis 3:15). It will take a second Adam–someone who obeys the covenant of works which Adam broke and who alone can redeem us from the guilt and power of sin–to undo the consequences brought upon us by the first Adam. This brings us to the incarnation of Jesus Christ, the person in whom God fulfills his promises and who is our Immanuel (God with us). The Word must become flesh if any of us are to be saved from the havoc wrought upon us by the first Adam (cf. John 1:17). There is no other way to rescue Adam’s fallen race from the guilt and power of sin.
The Old Testament is filled with various messianic prophecies, in which God’s promise to redeem his people are set forth with an amazing specificity.