Why did God become man?
In short: God became man to bring us back to Him, but not from a distance, by entering our life Himself all the way to the end. Saint Athanasius the Great says it in a phrase that has endured through the centuries, God became man so that man might become god, meaning to be filled with the life of God. He did not just send us a message, He came in person.
The Orthodox nuance
Think about the problem where it all starts. Man had cut himself off from God, and from this break death, fear, and sin entered the world. God could have forgiven us from above, with a word. But we did not just need forgiveness, we needed healing, someone to enter into our illness and heal it from the inside. That is why the Son of God truly becomes man, takes a body like ours, lives, hungers, weeps, dies.
And it is important that He truly became man, not just as a facade. Saint Gregory the Theologian used to say, what is not assumed is not healed. That is, if Christ had not truly taken on everything human, body, soul, will, then precisely that part would have remained unhealed. He took everything, to heal everything, except sin.
And the goal is not just for us to be forgiven, but to be lifted up. This is what Orthodox Christians call theosis (deification), a big word for a simple thing, man comes to be filled with God, like iron plunged into fire which remains iron, but becomes red and burns. Christ descends to us so that we can ascend to Him.
Sources
- John 1, 14 (the Word became flesh)
- Saint Athanasius the Great, On the Incarnation of the Word
- Philippians 2, 6-8 (He emptied Himself, taking the form of a bondservant)