What is the meaning of "muqt an-nafs fi dhatillah" (the loathing of the self in the essence of God)? May God reward you with the best reward.

Hating the self for the sake of Allah means disliking and belittling it, which leads to its rectification. This is a characteristic of the truthful ones (al-siddiqin). Hatred (al-maqt) is a strong dislike arising from something ugly. "For the sake of Allah" means in His path that leads to His pleasure. The opposite of this is blameworthy, which is loving the self, fulfilling its desires, and being pleased with it, which leads to its neglect.