Re: christianity?
I think a better understanding might be to look at the big picture (generically).
The creator is the [heavenly] origin of natural man. Because of what Adam and Eve (the earthly origin of natural man) did, the creator sent His Son to purify our souls so that we would be able to return to the/our heavenly origin after our bodies either wear out or are destroyed, in other words, the creator wants us back. The reason for the Holy Spirit (God's living character) is so we can learn to have the character of being Godly (Godly conscience) and treat each other with love (SHOW respect to each other, not just SAY it) and continue in the faith after we recieve salvation (Romans 11:22 "..provided you continue in His kindness to you, otherwise you too will be cut off").
Genesis 22:8 "Abraham said "God will provide [to] HIMSELF [His children/body] the lamb..." (God has a habit of providing a lamb for sacrifice as He did for Abraham).
Hebrews 9:9 "...cannot perfect the conscience..." (conscience must be pure, not just soul)
Hebrews 9:14 "...purify your conscience from dead works..." (If we are a good student of The Holy Spirit, we will most assuredly have a clear conscience).
When you look at Christianity by itself instead of seeing God's plan working through the Old Testament, it is easier to doubt what He did. The crucifixion was part of God's plan and leaving His spirit for us to learn from was also a necessary part of the plan.