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wa-lladhīna ʾāmanū wa-ʿamilū ṣ-ṣāliḥāti wa-ʾāmanū bi-mā nuzzila ʿalā muḥammadin wa-huwa l-ḥaqqu min rabbihim kaffara ʿanhum sayyiʾātihim wa-ʾaṣlaḥa bālahum
But those who have faith and do righteous deeds and believe in what has been sent down to Muhammad—and it is the truth from their Lord—He shall absolve them of their misdeeds and set right their affairs.
— Ali Quli Qarai
Surah Muhammad - Verse 2
2. But those who believe and do righteous good deeds, and believe in that which is sent down to Muhammad – for it is the truth from their Lord – He will absolve them of their vices and will make good their state.
Having faith is insufficient for availing oneself of Divine Favors rather one has to do good righteous deeds and follow the Messenger of God:
(“those who believe and do righteous good deeds and believe in that which is sent down to Muhammad”).
Regarding the Noble Verse in question exegets maintain that:
“But those who believe”
alludes to the Medinan Helpers (ansar) and “that which” (ma):
“in that which is sent down” (bi-ma nuzzila)
refers to the Qur’an; in other words the contextual meaning of the clause in question is “those who believed in the Qur’an sent down to Muhammad (S) by God and held that It is true, unchangeable, and standing firm on Its basis to the Last Day and It is not exposed to alterations like other Divine Books, e.g. the Torah, the Christian Bible, which have been abrogated by the Holy Qur’an. Those believing in the Qur’an and the prophethood of the Messenger of God, the Seal of the Prophets (S) and did righteous good deeds as per the Divine Decrees and Laws of the Islamic faith, God:
“will make good their state” (aslaha balahum),
namely their state will improve out of having faith in Islam, since their conversion to the Islamic faith and having faith in it will alter their inward states and refine their heart out of moral and inward vices and corruption.
“Will make good their state”
concerns believers and contrasts with:
“Will render their deeds vain”
which falls to the share of disbelievers. In other words, in as much as believers proceed on the path of improvement of their inward and outward states through their faith, disbelievers will remain in error out of their disbelief. It may also indicate that as disbelief will render good deeds vain, faith, au contraire, will lead to purity and refinement of heart.