Once you’ve neutered Scripture by telling it what it’s allowed to speak to us about—faith and practice, for example, but not science; sin and redemption but not history—you’re on a slippery slope.
But when a professing Christian writes
Does the saving power of Jesus vanish if sin becomes something that developed through natural history, rather than appeared all at once in the Garden of Eden?
…then he’s done. He’s not thinking Christianly in any meaningful sense. He’s no longer on a slippery slope; he’s jumped off a cliff.
If the Bible can’t tell us how sin entered the world, what can it tell us? Why must we believe in the “saving power of Jesus” if the Bible can’t be trusted to tell us what we need to be saved from?