Jesus is God.
Before the world was even formed, God had a plan for humanity.
That plan required the death of God.
Jesus left Heaven to live as a man.
Jesus lived on this earth perfectly, without sin.
Jesus took upon Himself the wrath of God for all sin ever committed.
Because Jesus stood in our place, dying for our sins, appeasing the wrath of God, we can be with Him through all eternity.
But why would Jesus need to do this in the first place?