What should a person do who committed immoral acts and theft in his youth, not knowing their impermissibility, then Allah guided him and he became righteous and Allah honored him by enabling him to memorize the Qur’an, but he always blames himself and remembers his sins when enjoining good and forbidding evil, and fears that these sins will prevent him from being a caller to Islam and a seeker of knowledge?

All praise is due to Allah, Who has accepted your repentance. Know that one who repents from sin is like one who has no sin. So, begin a new life with obedience to Allah and seeking knowledge, for good deeds erase bad deeds. Invite to Allah with wisdom and good counsel, and do not despair of Allah's mercy. Harming yourself is not permissible; what is permissible is to strive against your soul to obey Allah. Your repentance from theft is not complete unless you return the stolen item to its owner, or give it in charity on his behalf if you do not know him.