Tafsir of Al-Hijr 15:41

He (Allah, Glorified and Exalted be He) said: "This is a sirat 'alayya (path upon Me)," meaning a truth that I must uphold.

Mustaqim (Straight): There is no deviation in it, so one does not swerve from it toward anything else. The reference is to what the exception entailed, which is the salvation of the sincere ones from his (Iblis's) enticement. The word 'alayya (upon Me) is used for obligation. The Mu'tazila maintain this literally, based on their doctrine regarding the obligation of what is most beneficial upon the Exalted. The Ahl al-Sunnah said: Even though it is a grace from Him (Glorified and Exalted be He), it is likened to a binding truth due to the certainty of its establishment and the realization of its occurrence according to His promise (Glorified and Exalted be He); thus, 'alayya was used for that purpose. Or, the reference is to what the "sincere ones" (those who have attained sincerity) entails, in the sense that it is a path that leads to reaching [Allah] without crookedness or misguidance. It is similar to saying, "Your path is upon me," when one finishes traveling upon it. The preference for the preposition of superiority ('ala) over the preposition of termination (ila) is to emphasize the straightness and to testify to the elevation of the one who remains firm upon it, as it indicates more firmly the ability to reach [the destination]. It is a metaphor; therefore, there is no superiority over the Essence of Allah (Exalted be He far above that, with a great exaltation). 'Ala here does not mean ila (to). Yes, Ibn Jarir recorded from al-Hasan that he interpreted it as such, and he recorded from Ziyad ibn Abi Maryam and 'Abdullah ibn Kathir that they recited: "This is a straight path" (without 'alayya), and they said: 'Ala is ila and has the same status. The matter in this regard is simple, and it is linked to an implied verb "passes," while "path" entails it, so it is linked to it.

Some have said: The reference is to their division into two groups, meaning that this division—into one who strays and one who does not—is a matter whose outcome returns to Me, and it is not for you. The Arabs say, "Your path regarding this matter is upon so-and-so," meaning that the judgment regarding your affair returns to him. It is reported from Mujahid and Qatadah that this is a threat to the accursed one, just as you say to someone else, "Do what you wish, for your path is upon me," meaning, "You shall not escape me." Similar to this, according to al-Tabarsi, is the saying of Allah (Exalted be He): "Indeed, your Lord is in observation." The thing referred to in this view is what [Iblis] swore upon with emphasis. The most apparent of these viewpoints, as it has been said, is the first. [The author of] al-Bahr preferred that it means "to [the state of] sincerity." It was said: The most apparent [view] is that the reference is to what occurred in the statement of Iblis (upon him be the curse) when he said: "I will surely sit in wait for them on Your straight path. Then I will come to them from before them and from behind them..." etc. I do not know how it could be considered the most apparent.

Al-Dahhak, Ibrahim, Abu Raja', Ibn Sirin, Mujahid, Qatadah, Humayd, Abu Sharaf (freedman of Kindah), Ya'qub, and many others recited: ('Alin mustaqim) in the nominative case with tanwin, meaning "Lofty" (high) due to the loftiness of its status.