The old covenant with its laws, priests, tabernacle/temple, animal sacrifices, etc was a foretelling of what Jesus Christ would do. God was not unaware of the inadequacies of the Old Covenant and came up with a new plan to send Jesus as the perfect alternate. Jesus, as part of the triune Godhead, willingly took on flesh and became human with the goal of redeeming all of mankind. Heb. 8:6-8. Jesus was the prophesied "Son of God" who came to earth to live as a human. Why was it so important for Jesus to live as a man? God's law said "man" was to govern over the earth, so keeping to God's law, Jesus came in the form of man to save us. He also came to show us by example how we were originally intended to live before the fall of man. Jesus was tempted by Satan Luke 4:1-13 no differently than the way humans are to this day. Satan basically has no new tricks, unfortunately they still work on many people. I Cor.10:13

The devil hoped he could kill Jesus before He grew in power and spirit, but his plan failed as Jesus escaped and grew to be a man. Jesus began to take dominion over the devil, loosing many of the strong holds that Satan had held on mankind. Men's faith in God grew as Jesus forgave sins and healed lifelong invalids and took away disease with a word. Even those who were possessed by demons were set free, as demons were compelled to show themselves and declare Him the Son of God.

Satan worked in many ways to try and kill Jesus. Satan didn't realize Jesus' death was to be at God's appointed time and for God's appointed reason. He obviously wasn't aware of the consequences of the death of Jesus.

The Great Exchange:
The exchange consisted in Christ giving us freely what was His (righteousness, holiness, perfect standing, full obedience to the Law, etc.) and took our debt upon Himself. In order for God not to forsake us eternally (nor His Law), God forsook him ("My God, my God, what hast thou forsaken me ?"). By Jesus punishment we are made whole; by His stripes we are healed. The Lord laid on him the iniquity of us all. The reason Jesus had to die for our sins was so that we could live. Jesus is God in flesh (John 1:1,14; Col. 2:9) and only God can satisfy the Law requirements of a perfect life and perfect sacrifice that cleanses us of our sins.

Interesting Thought: How must have Satan felt when he realized by the death of Jesus and His ultimate resurrection, he had been stripped of his (illegal) power he had (illegally) taken from Adam and Eve. Satan now only has the use of lies, deception and evil.