Prevent all damage that would be dealt to you and creatures you control this turn.
Safe Passage doesn’t prevent damage that would be dealt to planeswalkers you control.
Safe Passage has no effect on damage that’s already been dealt.
Safe Passage prevents all damage, not just combat damage, that would be dealt to you and creatures you control this turn.
Safe Passage will prevent damage dealt to creatures that weren’t on the battlefield at the time it resolved.