Musar על חולין 181:19

There is another mystical dimension to the love between Esau and Jacob, or to love generally. Under certain conditions the feeling of love for something may transform evil into good and the קליפה, unworthy outer shell, may be transformed into something sacred. This is the very dimension which enables people to convert from paganism to Judaism. Our sages have connected this phenomenon with the גיד הנשה, when they explained Genesis 32, 27 where Samael says: "Let me depart, for dawn has come." Chulin 91a, has Jacob ask the angel: "Are you a thief or a gambler that you shun daylight? Samael responded that he was an angel and that from the day he had been created he had not had an opportunity to sing G–d's praises in the heavenly choir until that very day. Rashi interprets the word kubiestous in the Talmud to mean "soul snatcher." [I have translated it as "gambler." Ed.] There is a profound meaning in Rashi's comment, since souls are viewed as oppressed and held hostage by Samael. The Zohar in Parshat Mishpatim comments on this subject.