Maulana Ashraf Ali Thanvi (d. 1943 C.E.), wrote in his Quranic commentary Bayan ul-Quran, that by ad-deen is here meant ‘the principles of the deen’ (usul-e deen) that are common in all the shariahs of the different prophets—as for instance the oneness of God, prophethood, resurrection, and so on. This verse indicates, Maulana Thanvi said, that one must ‘keep this deen established’ (deen qaim rakhna) ‘and not change or abandon it’.
This same opinion is voiced by almost all other Quranic exegetes. Some of them have taken the term ad-deen in this verse to mean the beliefs common to the teachings of all the prophets, while some also include, in addition to these beliefs, certain practices or actions that come into being in people’s lives as a necessary result of these beliefs.
Thus, for instance, Abul Aliya (d. 708 C.E.) opined:
In this verse, iqamat-e deen means devotion to God alone and His worship.
Mujahid ( 722 C.E.) wrote:
God ordered every prophet to establish prayer, give zakat, acknowledge God and obey Him— and this is what iqamat-e deen is.
Abu Hayyan (d. 1344 C.E.) commented about iqamat-e deen in this context as follows:
It is a name for the beliefs held in common that are related to the oneness of God, obedience to God, faith in the prophets, faith in God’s books, faith in the Last Day and recompense for deeds.