How can one adhere to the teachings of religion while feeling that God has not forgiven past sins, and what are the conditions of repentance that erase transgressions?

Adherence to religion is not difficult for those for whom Allah has made it easy. Among the most dangerous pitfalls into which Satan casts a servant is despairing of Allah's mercy and losing hope in His forgiveness. Allah Almighty says: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" [Az-Zumar:53]. And Ya'qub (Jacob), peace be upon him, said: "And do not despair of the relief of Allah. Indeed, no one despairs of the relief of Allah except the disbelieving people." [Yusuf:87].

Sincere repentance and seeking forgiveness are obligatory, along with the certainty that Allah Almighty answers prayers, accepts repentance, and pardons evil deeds. Among what helps with adherence are: seeking refuge in Allah, disciplining oneself to obey and abandon prohibitions, seeking help from righteous companions, and staying away from places and companions of evil.