In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

إِنَّ رَبَّكَ وَٲسِعُ ٱلۡمَغۡفِرَةِ‌ۚ

Verily, your Lord is of vast forgiveness [53:32]

Had it not been for His forgiveness, the lands and the servants [i.e. its inhabitants] would have been destroyed. Had it not been for His forgiveness, the heavens would have collapsed on the earth and no living creature would have remained on it. [ref 1]

Neither Is The Believer Allowed to Lose Hope In The Mercy of Allaah Nor Be Complacent Regarding The Evil Consequences of Sins

Allaah [The Most High] said:

قُلۡ يَـٰعِبَادِىَ ٱلَّذِينَ أَسۡرَفُواْ عَلَىٰٓ أَنفُسِهِمۡ لَا تَقۡنَطُواْ مِن رَّحۡمَةِ ٱللَّهِ‌ۚ إِنَّ ٱللَّهَ يَغۡفِرُ ٱلذُّنُوبَ جَمِيعًا‌ۚ إِنَّهُ ۥ هُوَ ٱلۡغَفُورُ ٱلرَّحِيمُ

وَأَنِيبُوٓاْ إِلَىٰ رَبِّكُمۡ وَأَسۡلِمُواْ لَهُ ۥ مِن قَبۡلِ أَن يَأۡتِيَكُمُ ٱلۡعَذَابُ ثُمَّ لَا تُنصَرُونَ

وَٱتَّبِعُوٓاْ أَحۡسَنَ مَآ أُنزِلَ إِلَيۡكُم مِّن رَّبِّڪُم مِّن قَبۡلِ أَن يَأۡتِيَڪُمُ ٱلۡعَذَابُ بَغۡتَةً۬ وَأَنتُمۡ لَا تَشۡعُرُونَ

أَن تَقُولَ نَفۡسٌ۬ يَـٰحَسۡرَتَىٰ عَلَىٰ مَا فَرَّطتُ فِى جَنۢبِ ٱللَّهِ وَإِن كُنتُ لَمِنَ ٱلسَّـٰخِرِينَ

أَوۡ تَقُولَ لَوۡ أَنَّ ٱللَّهَ هَدَٮٰنِى لَڪُنتُ مِنَ ٱلۡمُتَّقِينَ

أَوۡ تَقُولَ حِينَ تَرَى ٱلۡعَذَابَ لَوۡ أَنَّ لِى ڪَرَّةً۬ فَأَكُونَ مِنَ ٱلۡمُحۡسِنِينَ

بَلَىٰ قَدۡ جَآءَتۡكَ ءَايَـٰتِى فَكَذَّبۡتَ بِہَا وَٱسۡتَكۡبَرۡتَ وَكُنتَ مِنَ ٱلۡكَـٰفِرِينَ

Say: “O ‘Ibadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allah, verily Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful. And turn in repentance and in obedience with true Faith (Islamic Monotheism) to your Lord and submit to Him, (in Islam), before the torment comes upon you, then you will not be helped. And follow the best of that which is sent down to you from your Lord (i.e. this Qur’an, do what it orders you to do and keep away from what it forbids), before the torment comes on you suddenly while you perceive not!” Lest a person should say: “Alas, my grief that I was undutiful to Allah (i.e. I have not done what Allah has ordered me to do), and I was indeed among those who mocked [at the truth! i.e. La ilaha ill-Allah (none has the right to be worshipped but Allah), the Qur’an, and Muhammad and at the faithful believers, etc.] Or (lest) he should say: “If only Allah had guided me, I should indeed have been among the Muttaqun (pious and righteous persons); Or (lest) he should say when he sees the torment: “If only I had another chance (to return to the world) then I should indeed be among the Muhsinun (good-doers). Yes! Verily, there came to you My Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.) and you denied them, and were proud and were among the disbelievers.

Repentance:

https://salaficentre.com/2019/08/the-obligation-of-repentance-especially-during-calamities-and-afflictions-by-imaam-abdul-azeez-bin-baaz-rahimahullaah/

https://salaficentre.com/2019/09/brief-commentary-on-a-tremendous-supplication-related-to-repentance-by-imaam-abdul-azeez-bin-baaz-rahimahullaah/

http://www.salaficentre.com/2015/07/allaah-afflicts-mankind-with-different-types-of-afflictions-because-of-their-disobedience-and-wicked-deeds/

[Ref 1: An excerpt from Tayseer al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan). Publisher: Daar Ibn Hazm 1^st Ed 1424AH (2003). Translation slightly paraphrased]

[Ref 2: Surah Az-Zumar Aayaat 53-59