The English language does not do justice to the Arabic word Niʿmah which appears in the Qur’an in many places. However, the common words used interchangeably are bounty, favor, grace, blessing or mercy.
In most people’s mind, the meaning of Niʿmah is every kind of good which brings happiness, pleasure or enjoyment. However, Niʿmah can be relative as it can bring pleasure to one person and yet a misfortune to another.
According to al-Mizan, the Divine favor and bounty is the thing which has an affinity with the nature of the recipient of that bounty. All the things are interconnected with each other because they are parts of the system of Divine management and in the long run all have affinity with one another. Most, rather all of them are Divine bounties when they are placed parallel to each other. Allah says: And He gives you of all that you ask Him; and if you count Allah's favors, you will not be able to number them; most surely man is very unjust, very ungrateful. (14:34)
The Qur’an shows, through many verses, that the things which are counted as Divine favors or bounties would really be bounties when they conform with the Divine purpose for which they were given to man. They have been created to serve as a Divine help to man in order that he could use them in the way of his real felicity; in other words, when they help the man get nearer to Allah through worship and submission to His Mastership. All the things and faculties which the man uses with the aim of attaining nearness to Allah and seeking Divine pleasure are the bounties and favors. Otherwise, they will become an affliction and trial. Allah says: And when your Lord made it known: If you are grateful, I would certainly give to you more, and if you are ungrateful, My chastisement is truly severe. (14:7)
Islam is a religion because it is a collection of what was sent down from Allah for the guidance of His servants, so that they may worship Him properly; and it is a Divine favor and bounty in as much as practically it contains in itself the wilayah of Allah, the wilayah of His Messenger and of those vested with authority (ulu 'l-amr) after him. The wilayah of Allah (that is, His management of the servants' affairs through the religion) cannot be complete except through the wilayah of His Messenger; nor will the wilayah of His Messenger be complete without the wilayah of those vested with authority after him; and that wilayah means their management of the religious affairs of the ummah with Divine permission. Allah says: O you who believe! obey Allah and obey the Messenger and those vested with authority from among you (4:59), Again, Allah says: Only Allah is your guardian and His Messenger and those who believe, those who keep up prayers and pay the zakat while they bow (5:55).
Now, when we examine the following verse, This day have those who disbelieve despaired of your religion, so fear them not, and fear Me. This day have I perfected for you your religion and completed My favor on you and chosen for you Islam as a religion...(5:3), we realize that the favor mentioned in the verse is the Divine favor of wilayah.
Regarding the above verse (5:3), Allamah Tabataba'i says:
The verse means: This day, and it is the day when those who disbelieve have despaired of your religion (that is, have lost all hopes in your religion), I have perfected for you the whole religious perceptions (which I had revealed to you before) by making the wilayah obligatory for you; and I have completed My bounty on you, and it is the (bounty of) wilayah which means management of the religious affairs with Divine guidance. Until now, you were under the wilayah of Allah and His Messenger only; but it could work only up to the time the revelations would be coming down from Allah; it could not work later when the revelation would be cut off, when the Messenger would not remain among the people to safeguard the Divine religion and defend it. It was essential that someone (like the Messenger) should be appointed to carry on this responsibility and be vested with the authority after the Messenger of Allah, to act as the overall authority in the affairs of the religion and the ummah.
The above is an excellent explanation by the author of tafsir al-Mizan.
The said appointment of someone like the Messenger (that is, Ali b. Abi Talib) to carry on the management of the affairs of the religion and the ummah was carried out by the Messenger upon the instruction received from Allah as mentioned in the following verse: O Messenger! deliver what has been revealed to you from your Lord; and if you do it not, then you have not delivered His message, and Allah will protect you from the people; surely Allah will not guide the unbelieving people. (5:67)
Ref: Tafsir al-Mizan, Eng. Vol. 9 (Pub. WOFIS).