Commentary
Verse 53 opens with the words: قُلْ يَا عِبَادِيَ الَّذِينَ أَسْرَفُوا (0 servants of Mine who have acted recklessly against their own selves, do not despair of Allah's mercy. Surely, Allah will forgive all sins.). Taba` i, Said Ibn Jubayr reports from Sayyidna Ibn ` Abbas ؓ that there were some people who had killed a lot of people unjustly and had committed a lot of shameful acts. They came to the Holy Prophet ﷺ and submitted before him, 'The religion you invite us to is, no doubt, very good, but we have a problem. We think about all those major sins we have already committed. Now if we were to become Muslims, do you hope that our repentance will be accepted?' Thereupon, Allah Ta’ ala revealed this verse to the Holy Prophet ﷺ - reported by al-Bukhari in that sense (al-Qurtubi).
Therefore, the outcome of the subject taken up in the verse comes to be that, well before death arrives, the repentance made from sins, no matter how serious, even from kufr (disbelief) and shirk (ascribing of partners to Allah), gets to be accepted. And by virtue of a genuine taubah (repentance), all sins will be forgiven, therefore, no one should lose hope in the mercy of Allah.
Sayyidna ` Abdullah Ibn ` Umar ؓ said that, out of all verses of the Qur'an, this verse brings the strongest message of hope for sinners. But, Sayyidna Ibn ` Abbas ؓ said that the strongest such verse is: إِنَّ رَبَّكَ لَذُو مَغْفِرَةٍ لِّلنَّاسِ عَلَىٰ ظُلْمِهِمْ (And surely, your Lord is the lord of forgiveness for the people against their wrongdoings - Ar-Ra'd, 13:6)