Does Allah forgive heinous sins and grave transgressions, and accept repentance, and is one act of repentance for them sufficient for entry into Paradise? And is merely uttering the two Shahadas enough for faith? And with what does one begin returning to Allah and committing to His path? And what is the way to persist therein? And will Allah erase sins?

If one repents with sincere and truthful repentance, Allah accepts their repentance and forgives their sins, no matter how great they are, for Allah the 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.'" (Quran 39:53) And the Prophet, peace and blessings be upon him, said: "The one who repents from sin is like one who has no sin."

To remain steadfast on the path of Allah, you must obey His commands and avoid His prohibitions, maintain the obligatory acts of worship, increase in supererogatory acts, accumulate good deeds that expiate bad ones, seek help from the company of righteous people, and ponder upon the names and attributes of Allah, death, and what comes after it. This softens the heart and strengthens steadfastness. You are not required to utter the two testimonies of faith unless you have committed an act that nullifies your Islam.