Prerequisites and Conditions of Taubah: #1 - Knowledge:

A prerequisite to repentance is knowledge and the admission of sin; for ignorance and denial are barriers, preventing return. Knowledge of the Halaal and the Haraam, as well as the consequences of sin, both in this world and in the next, will make one most anxious to escape the result of his carelessness. And where can he find refuge and protection from that except with Allaah سبحانه و تعالى? Therefore, one should consider the reason he fell into sin, which is that he, temporarily, forgot Allaah سبحانه و تعالى

On the authority of Al-Numan bin Basheer, who said : I heard the Messenger of Allaah صلى الله عليه وسلم say : "That which is lawful is plain and that which is unlawful is plain and between the two of them are doubtful matters about which not many people know. Thus he who avoids doubtful matters clears himself in regard to his religion and his honor, but he who falls into doubtful matters falls into that which is unlawful, like the shepherd who pastures around a sanctuary, all but grazing therein. Truly every king has a sanctuary, and truly Allah's sanctuary is His prohibitions. Truly in the body there is a morsel of flesh which, if it be whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart." [Bukhari and Muslim]