Shaykh al-Islām, may Allah Most High have mercy on him, also said:

A Principle Concerning Unity and Division, Their Cause and Consequence

Allah Most High said:

“He has ordained for you in religion what He enjoined upon Noah, that which We have revealed to you, and what We enjoined upon Abraham, Moses, and Jesus: establish the religion and do not become divided in it.”

He, glorified is He, tells us that He has ordained for us what He enjoined upon Noah, what He revealed to Muhammad, may Allah bless him and grant him peace, and what He enjoined upon the three others mentioned. These are the messengers of firm resolve from whom the covenant was taken, as stated in His words:

“And when We took from the prophets their covenant, and from you, Noah, Abraham, Moses, and Jesus, son of Mary.”

In His words:

“what He enjoined upon Noah, that which We have revealed to you, and what We enjoined,”

He used the relative pronoun alladhī (“that which”) and the wording of revelation in reference to Muhammad, whereas for the other messengers He used the wording of “injunction.”

Then He said:

“Establish the religion.”

This explains the injunction. Here, (an) is the explanatory particle that follows a verb conveying the meaning of saying without itself being a form of the verb “to say,” as in His words:

“Then We revealed to you: follow,”

and:

“We enjoined upon those who were given the Scripture before you, and upon you: fear Allah.”

The meaning is: We said to them, “Fear Allah.” Likewise, His words, “Establish the religion,” have the sense of His saying: “The religion prescribed for you is what He enjoined upon messengers; We said, ‘Establish the religion and do not become divided in it.’” Thus, what has been ordained for us is what was enjoined and revealed, namely:

“Establish the religion.”

Thus, “Establish the religion” explains