Verily Allah can forgive all the sins! Do we need to doubt the mercy of Allah SWT? No not at all. A human being is prone to the evil thoughts as Satan is working all the time to misguide and mislead the servant and slaves of Allah SWT. Allah's mercy is limitless, He can forgive anyone and anytime who He wants.
Allah SWT asks the Prophet SAW to say to the slaves of Allah (Abd: one who submits to Allah SWT) who have committed sins and have performed evil deeds not to despair of the mercy of Allah. Allah's mercy is huge. There are many ayahs in Quran where Allah's mercy and forgiveness are mentioned. Yet I report here only one ayah from Surah Az-Zumr 39, Ayah 53 wherein Allah SWT says:
Surah Az-Zumr 39: Ayah 53
قُلۡ يٰعِبَادِىَ الَّذِيۡنَ اَسۡرَفُوۡا عَلٰٓى اَنۡفُسِهِمۡ لَا تَقۡنَطُوۡا مِنۡ رَّحۡمَةِ اللّٰهِ ؕ اِنَّ اللّٰهَ يَغۡفِرُ الذُّنُوۡبَ جَمِيۡعًا ؕ اِنَّهٗ هُوَ الۡغَفُوۡرُ الرَّحِيۡمُ
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 the sins. Truly He is Oft-Forgiving, Most Merciful"
In this ayah, Allah SWT informs clearly that with His Mercy He forgives all the sins. This definitely is true but Allah SWT also says in the next ayahs that a transgressor abd needs to be repentant and obedient to Allah and submissive to Him before he meets the torment (azaab) of Allah SWT.
Allah SWT describes the people who might be shocked with the torment as they didn't perceive that it will strike because they did not repent, became obedient and submitted to the will of Allah. These people when struck with torment would say either (1) I was undutiful to Allah and I mocked at the truth (La ilaha illallah, the Quran, Prophet Muhammad SAW and at the faithful believers) or (2) if only Allah had guided me I would have become one of the Pious/Muttaqun or (3) if I had another chance I would have become one of the Mohsinin. (Refer to 39:56-58).
Therefore, it is important to make ourselves aware of the fact that Allah's all attributes are infinite. Moreover, we must always seek the mercy of Allah SWT in all cases be it seeking forgiveness, seeking protection, seeking favors, seeking anything.
May Allah SWT have mercy on all of us. Ameen
