Siman 66

(7.) Pertaining to the matter printed at the end of the Legendary Tales [Sichos HaRan], which begins: "Know that there are two kinds of palaces — in one dwells a king and in one dwells a slave etc." — when one serves G-d and is still in the aspect of slave, he is still in the aspect of cursed, G-d forbid. And there is the aspect of slave in holiness, the aspect of Moses, servant of G-d. And know that there is a commandment through which one exits from the aspect of slave — and it is the commandment of redeeming captives.