Further thinking on the purpose of Jesus’ death, being inspired by this article while reading it right now, I propose this theory:

Christ’s death was to demonstrate that an altruistic person will be rewarded (as in Christ’s resurrection and power over the entire heavens given) justly, even when at first it seems that this way leads to death.

This has shown to the heavenly powers that altruism works and leads to life rather than to death as someone may expect.

And this needs a sacrifice of God himself, because it is necessary to show that even the highest level of altruism is rewarded.