You know that he appeared … and in him there is no sin.
— 1 John 3:5
I glorified you on earth, having accomplished the work that you gave me to do.
— John 17:4
Our chief end speaks also of our chief sin. The basic principle of sin is idolatry, the worship of something other than God—the glorifying and enjoying of something chiefly other than God.
The Psalm says, “There is none who does good” (14:1). Man seeks not after God but after his own self-adoring will. Isaiah says, “we have turned—every one—to his own way” (53:6). Man naturally rebels against God as his King; thinking, desiring, living and doing, in principle as the ancient people of Israel, of whom it is said, “In those days there was no king in Israel. Everyone did what was right in his own eyes” (Judges 17:6).
Christmas is a reminder that God came to glorify God, even, and especially, where man failed. Jesus said, “For I have come down from heaven, not to do my own will but the will of him who sent me” (John 6:38). And again, “My food is to do the will of him who sent me and to accomplish his work” (John 4:34). Jesus repeatedly draws attention to the fact that He came and was sent to glorify God through perfect obedience to the will of the Father. Before John the Baptist, Jesus affirmed, “it is fitting for us to fulfill all righteousness … and behold, a voice from heaven said, ‘This is my beloved Son, with whom I am well pleased’” (Matthew 3:15–17). This was part of His mission. Jesus said Himself that He was sent and lived a life marked by intimacy with the Father. Regarding His coming and living, He said, “I always do the things that are pleasing to him” (John 8:29). Hebrews reminds us that when “Christ came into the world, he said, ‘Sacrifices and offerings you have not desired, but a body have you prepared for me . . . Behold, I have come to do your will’” (Hebrews 10:5–7).
Where Adam failed to glorify God in his life lived on earth—where Israel failed, where you and I fail—Christ came to perfectly fulfill. In His life on earth, Jesus lived under the afflictions of sin’s consequences, yet He Himself was without sin. Where Adam failed to live right under perfect conditions, Christ lived perfect under cursed conditions. He suffered deep humiliation and anguish of soul—even before the cross—to glorify His Father in one perfect life (Isaiah 53:3; John 11:33, 35, 38; Matthew 26:38; Luke 19:41; 22:44; Hebrews 4:15; 5:7). Where the life of Adam brought a curse on the world, Christ lived and died to undo, invert, and reverse that curse through His substitution. The penalty of our rebellion and belittling of God, Christ came to absorb and take away through His death. But not only this, He came to earth first as a baby—the incarnation doesn’t begin at the cross. Christmas reminds us also that Jesus took on human flesh to magnify the worth of God through His life lived on earth.
Why the incarnation? Why the God-man? One reason was to glorify God in perfect life.