Or HaChaim on Genesis 37:21/אור החיים על בראשית ל״ז:כ״א

1 ויצילהו מידם. "He saved him from harm at their hands. This action was applauded by the Torah as man is a free creature possessing freedom of choice and able to kill people who are not guilty or have not been convicted, as distinct from wild beasts which do not kill humans unless the latter are guilty of death in the eyes of G'd. The words ויצילהו מידם mean that he saved them from the evil consequences of carrying out their freedom of choice to kill. By doing what he did Reuben nullified the brothers' statement: "we shall see what happens to his dreams."

2לא נכנו נפש. "Let us not kill him." What Reuben meant was "let us not kill him outright ourselves but only cause his death indirectly." When he said later: "do not shed blood, throw him into the pit," this was his argument to his brothers. He only pretended to agree that Joseph's death should be caused because he could think of no other way of saving Joseph's life and restoring him to his father. He was quite certain in his own mind that no wild beast would harm Joseph, or any other of Jacob's sons for that matter. He himself would also not allow Joseph to remain in the pit long enough to die of hunger. Proof of Reubens' intention is that the Torah reports that he returned to the pit shortly after the brothers had sold Joseph in his absence. He had planned to take Joseph out of the pit.