In the Body

God did what the law could not do. He sent his own Son in a body like the bodies we sinners have. And in that body God declared an end to sin’s control over us by giving his Son as a sacrifice for our sins. – Romans 8:3

Why did He have to come in the flesh? 

And I know that nothing good lives in me, that is, in my sinful nature.  I want to do what is right, but I can’t. – Romans 7:18

Because our flesh is weak and it is impossible to be saved or reconciled to God in the flesh, Jesus had to come as we are.

Because God’s children are human beings—made of flesh and blood—the Son also became flesh and blood.  For only as a human being could he die, and only by dying could he break the power of the devil, who had the power of death.  Only in this way could he set free all who have lived their lives as slaves to the fear of dying. – Hebrews 2:14-15

The flesh allowed Him to die.  Just as it will allow all of us to die.  The flesh cannot save.

We also know that the Son did not come to help angels; he came to help the descendants of Abraham.  Therefore, it was necessary for him to be made in every respect like us, his brothers and sisters, so that he could be our merciful and faithful High Priest before God.  Then he could offer a sacrifice that would take away the sins of the people. – Hebrews 2:16-17

Jesus was more than just flesh, He was our Holy Priest, making the highest sacrifice for the atonement of our sins. But by being in the flesh and not sinning, He could offer what we can’t, a sinless body.  He could offer the perfect sacrifice, one that could be acceptable to God and therefore death would no longer be an eternal separation from God.

He is the kind of high priest we need because he is holy and blameless, unstained by sin.  He has been set apart from sinners and has been given the highest place of honor in heaven.  - Hebrews 7:26

That is why, when Christ came into the world, he said to God, “You did not want animal sacrifices or sin offerings.  But you have given me a body to offer.” – Hebrews 10:5

And by sacrificing His sinless flesh, “God did what the Law could not do” and “declared an end to sin’s control over us”, specifically sin’s control over our eternal destiny.