Imam As-Sadiq (‘as) said:
The meaning of the quality of faith is the declaration, submission to God and seeking His favors through the declaration, and the fulfillment to Him through having knowledge of every obligatory matter, whether big or small, beginning with the outline of God’s oneness up to the last chapter of obedience without missing anyone. All this should be connected and matched up to each other. If a servant fulfills what is imposed upon him according to what we have recently explained, he will then deserve the quality of faith and will deserve the reward duly.
This is because the meaning of faith is the declaration, and the meaning of declaration is the sincerity of obedience. This proves that obedience as a whole is related to each other. A believer loses the quality of faith only when he ignores the matters due to which he deserved to have that quality. He deserved the name and meaning of belief meritoriously only when he fulfilled the grand duties connectedly and neglected and avoided the disobediences. He also will not abandon the quality of faith when he commits insignificant acts of disobedience to God and ignores the insignificant acts of obedience. God says:
If you avoid the grand violating that which has been prohibited, your sins will be forgiven and you will be admitted into an exalted dwelling. (4:31).
This holy saying proves the fact that we have recently indicated. Accordingly, forgiveness is obtained when the grand sins are avoided. If a grand sin is committed, all of the acts of disobedience, whether grand or insignificant, will be taken in the consideration of judgment. Hence, castigation and penalty of all the acts of disobedience (to God) will fall. This is the quality of faith and the quality of a believer who deserves the reward duly.