[4:31] If you avoid the grave sins that are forbidden you, We will absolve you of your evil deeds and admit you by an honorable gate.
The grave sins here, in scholarly terms, are those of polytheism. According to the explanation of allusion, they [also] include acts of hidden polytheism. In that group is paying heed to creatures, seeking the pleasure of their acceptance, courting their affection, and shutting one's eyes to the right and reality (ḥaqq) of God because of them.
It is said that when one has committed to the covenant, one is kept from being charged with disbelief in one's transgressions.
It is said the worst of the grave sins is your affirmation of your self. When you have experienced its negation you will be delivered from the captivity of tribulations. We will admit you in your affairs by an honorable gate, a beautiful admission. You will no longer see your comings and goings as coming from yourselves but rather you will see the One who has free disposal over your affairs.