How does his death save us from death?
Evil exists, that part is pretty clear.
There is that problem of evil I found out about on this forum.
My explanation is a god was assigned this planet and maybe not just this planet but any planet people lived on, and he was serving the role of god for anyone meeting a god or wanting to know a god for whatever reason.
At some point the God who created the universe and had theses various gods serving different functions, understood that this god over all people was being corrupted by having such an exalted position and in the absence of a seeable god, this lower god could think of himself as the most high god. This apparent god of the internal affairs of the universe was given warnings from the one actual supreme being to stop it. He refused and just continued on as he had been gradually more and more, headed. The supreme being could not just kill the god of the world without some negative repercussions so he quarantined him to one planet as a type of exile, to prevent a universal infection of his devious nature into all the lesser gods.
This person on this planet would be who we would call today Satan and he saw the writing on the wall that he was going to end up being done away with so instead of repenting decided to take hostages hoping to force God not to kill him. The idea being that if he could get all mankind to defect from God to Satan's camp God would have to relent on the whole death thing, at least for Satan's case, which being Satan was all he really cared about anyway.
During all of this, there was another person who was somehow the son of the Supreme being who cared about the future of all these people and decided to do something about it. He set aside his god attributes and became a human being born in an ordinary sort of way as in vaginal birth from a woman of this world. Somewhere along this road, or maybe all along, there was a spark of awareness in this Son of God that at one time he was something other than a normal person and was for all intents and purposes, God. Not actually being a god at this point but retaining a spiritual link of communication to his Father God, the son was able to maintain an existence on this planet and living in this world without having committed a sin that would have warranted a death penalty.
Satan eyeing the son, Jesus with contempt and envy, wanted to claim him also as a hostage and tempted him by being offered a godhood in his system. being frustrated in these attempts Satan turned his tactic to murder along with his claim to taking possession of his person on account of being a member of this accursed race.