Mankind had gone astray. Sin and death and he who had the power of death, the devil, had come to power because of the fall into sin, so that our bodies had become slaves of unrighteousness. So something had to happen.
“Who, being in the form of God, did not consider it robbery to be equal with God, but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men. And being found in appearance as a man, He humbled Himself and became obedient to the point of death, even the death of the cross.” Phillipians 2:6-8
He came to earth in a human body. His human nature was like ours. Why? Because He actually had to experience what it means to be human in order to condemn the sin which mankind has been bound to. He experienced it and overcame it and in this way overthrew the devil and took his power away.