Man knows best of himself

I heard Abu Abdillah Ja’far ibn Muhammad, peace be upon both, say: "No benefit is derived by a slave of Allah who makes a show of being good, while inwardly he is vicious and evil. Does his inner self not tell him that he is not what he pretends to be? And (also), Allah, Most High, says (in the Qu’ran): ’Rather, man has a keen insight of himself’ (75:14). Surely, when the inner self of a person is reformed, his external self gains strength." May Allah bless our master Muhammad, the Prophet of Makkan origin and upon his pure progeny, and salutations.