You have to understand what death is... In God's presence, all is sustained. Without, all is subject to death and decay. God, the absolute authority, cannot justly tolerate disobedience therefore the wages of sin is death. Christ did not sin, and yet was subject to death. He was forsaken that dark day, as far as his human frame could tell. It was an infinite injustice, yet by it we are "in" him eternally. He was made responsible for our sin, bearing the consequences so that all who are in him could be spared. The passover atonement was established as a pattern for thousands of years prior, and was absolutely necessary for anyone to be able to come before God, as we do now. He was the lamb of God, and from our angle, is all of God that we can see, God with Us.