It's true that if God were absolutely "fair," no one would be saved.
After all, he created humans and set a wonderful future before them, asking almost nothing in return. And the first humans chose to defy him. So, what's his responsibility towards that which he himself had brought into existence?
If any of us were to make a nice place for our pet, only to have the pet then ruin it for any reason, we wouldn't think that we have a moral obligation to rebuild it or make another one just like it.
If we were very kind, we might decide to follow-up by doing basically what God did in the case of humanity, but it would not be unfair of us if we chose not to do so.
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