Rabbi Yitzḥak said: He [Isaac] sought to curse him [Jacob]. The Holy One blessed be He said to him: ‘Be careful, if you curse him, you are cursing yourself, as you said: “Cursed be one who curses you”’ (Genesis 27:29). Rabbi Levi said: Six items serve a person; three are in his control, and three are not in his control. The eye, the ear, and the nose are not in his control – he sees what he does not wish, he hears what he does not wish, and he smells what he does not wish.
The mouth, the hand, and the foot are in his control – [the mouth,] if he wishes he toils in Torah; if he wishes, [he speaks] evil speech; if he wishes, he curses and blasphemes. The hand, if he wishes, he performs a mitzva; if he wishes, he steals; if he wishes, he kills. His foot, if he wishes, he goes to theaters and circuses; and if he wishes, he goes to synagogues and study halls. When he merits, the Holy One blessed be He renders the ones in his control to be not in his control.
The hand – “his hand that he had extended toward him shriveled” (I Kings 13:4); the mouth, “indeed, he shall be blessed” (Genesis 27:33); the foot, “My son, do not walk on the way with them…for their feet run to evil” (Proverbs 1:15–16).