David Burnette on 4 reasons from Hebrews for the incarnation:
You'd be hard-pressed to come up with a greater and more glorious mystery than the incarnation. That God took on human flesh is a truth worthy of our deepest gratitude, wonder, and adoration. However, as we reflect on this mystery, my guess is that most of us haven't spent much time thinking about why God took on flesh. Sure, He was demonstrating his infinite love, but why did he do it this way?
The Bible answers this 'why' question from different angles, but I want to point you to four reasons for the incarnation from a book we don't normally associate with Christmas - Hebrews. The author of Hebrews tells us that Jesus shared in our "flesh and blood" (2:14), and it gives us four purposes for this glorious reality in Hebrews 2:14-18:
"Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery. For surely it is not angels that he helps, but he helps the offspring of Abraham. Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people. For because he himself has suffered when tempted, he is able to help those who are being tempted."
According to this passage, the Son of God came in the flesh...
1. To Destroy the Devil (v. 14)Ever since the Fall, the devil has tempted men to sin and led them down a road of destruction. But Christ broke the devil's stranglehold on death by dying. This sinless man took the punishment for sin that only a man could take (14). He destroyed the devil, and the cross was his weapon. One day that destruction will be evident to all (Rev 20:10).
2 To Deliver Lifelong Slaves (v. 15)We are enslaved by the fear of death and the coming judgment. Whether we admit it or not, we know our sin will find us out. But Jesus removed that enslaving fear by tasting death for us (Heb 2:9). Because he has absorbed God's wrath, the devil can no longer hold this harrowing fate over our heads. For those who belong to Christ, the tables have turned: death is gain (Phil 1:21). We are free.
3. To Be a Merciful and Faithful High Priest (v. 17)By being made like us, Jesus can sympathize with our weaknesses (Heb 4:15). He knows what it is like to be tempted and to suffer as a man. He was also able to demonstrate his faithfulness by his unswerving and glad obedience to the Father while on earth (Heb 3:2). As his people, we have every reason to trust such a high priest.
4. To Make Propitiation for the Sins of His People (v. 17)A propitiation is an atoning sacrifice, and that's exactly what Jesus offered when he died on the cross. He removed our sin and the wrath we had incurred. Making sacrifices is what all priests do, but this high priest gave his own life for the sins of his people. Christ's death provides for us the forgiveness of sins and the promise of eternal life.
Much more could be said from Hebrews and from other places in God's Word about why Jesus came in the flesh. But for now, these four reasons from Hebrews 2:14-18 should give us enough to be thankful for to last a good while. Understanding not only that Jesus came in the flesh but also why he did gives us all the more reason to love and worship him.