How can one differentiate between what is lawful and unlawful, how can one atone for kissing a forbidden person and speaking indecently with them, and how can one return to obedience to Allah?

The way to discern what is lawful (halal) from what is unlawful (haram) is through deep understanding (fiqh) of Allah's religion. The Prophet, peace and blessings be upon him, clarified that "The lawful is clear, and the unlawful is clear, and between them are doubtful matters." Scholars distinguish between these categories either through textual evidence or analogical reasoning (qiyas).

As for what results from disobedience (ma'siyah), the obligation is to promptly engage in sincere repentance (tawbah), characterized by remorse and a firm resolve not to return to the sin, along with frequent seeking of forgiveness (istighfar) and performance of good deeds (ta'at). If repentance fulfills its conditions, then Allah accepts it and transforms evil deeds into good ones. One must also beware of obsessive thoughts (waswas) and delusions, and strive against the self (nafs) to remain steadfast.