Does the ruling of the verse: "Whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely. And whoever saves one - it is as if he had saved mankind entirely" apply to us, and what does "saves one" mean?

The verse includes the Children of Israel and others. Commentators have interpreted the phrase "and whoever saves a life" with five opinions: saving it from destruction, or refraining from killing a forbidden soul, or pardoning retaliation (qisas), or deterring killing, or assisting the guardian (wali) in exacting retaliation. They interpreted "it is as if he had saved all of mankind" to mean that he receives the reward of one who saved all of mankind, or that people are obliged to thank him. "Reviving" here is a metaphor that includes refraining and saving from destruction. The similitude in the aspect of killing is to emphasize its horror, and in the aspect of reviving, it is to encourage pardon and saving from destruction, including saving from injustice if it leads to destruction.