This is in essence how I understand it:
God created humanity and set the first two people in the Garden of Eden, where they were instructed not to eat fruit from the Tree of Knowledge. They disobeyed, and as a result they were cast out of paradise, in the event described as the Fall of Man (incidentally, Genesis also suggests that they were cast out to prevent them from eating from the Tree of Life and achieving immortality see Gen 3:22). The Fall of Man was accompanied by something known as "Original Sin," which ranges from Reformation "total depravity" to some lesser inclination to evil, as in Eastern Orthodoxy, and also the introduction of death.
So now humanity dies, women experience pain in childbirth, man must work the soil, etcetera. Man's inclination to sin (again the Christian interpretation) is recorded throughout the Hebrew scriptures, from the first murder to the Flood to the destruction of the cities of the plain, Sodom and Gomorrah. As this human drama unfolds, there are a series of covenants, in the form of mutual contracts or promises, that God makes with individuals and collectives (Abrahamic, Mosaic, etc.).
Now this is where it gets very tricky because you have modern reinterpretations and some differences between the various sects, but in essence the role of Jesus as the Christ is to reconcile fallen man and God. Jesus can achieve this because of his status as the incarnation of God, more or less. And this reconciliation involves, among other things, the defeat of death. So Jesus was "sacrificed" to reconcile God and man, and offer the hope of eternal life, and the defeat of death.
So to review: God creates man, who disobeys God causing entry of sin into the world. God casts man out of Paradise, and he toils and dies as a result of this sin. To eradicate the power of sin, including death, God incarnates in a human being named Jesus, who is killed by crucifixion. After being killed, God waits three days and resurrects this Jesus character, therefore demonstrating power over death and sin, and promising eternal life to those who believe in the resurrected God King Jesus.
It would seem clear to me that God sacrifices himself, to reconcile himself to mankind, a division that he more or less caused by punishing Adam and Eve for their sin in the garden. Does this sound implausible and unnecessarily convoluted? I think so, but that is the essence of mainstream Christianity.