Tafsir of Az-Zumar 39:12

That is: I have been commanded to do that so that I may be the foremost of the Muslims in this world and the Hereafter. This is because attaining the vanguard in religion is achieved through sincerity within it, and his sincerity—upon him be prayer and peace—is more perfect than the sincerity of any other sincere person. Therefore, "the first" here refers to primacy in honor and rank.

The conjunction (the lam in li-an) is used because the second statement differs from the first by qualifying it with the cause, signaling that the aforementioned worship, just as it demands being commanded for its own sake, also demands it for what necessarily follows it: precedence in religion.

The Basrans, in this verse and its like, hold that the object of the command is omitted and that the lam is causative. Others argue that it is za’idah (redundant/extra), citing as evidence its omission in the Almighty’s saying: "And I have been commanded that I be of the Muslims," "And I have been commanded that I be of the believers," and "And I have been commanded that I be the first of those who submitted." Yet, all of these remain consistent with an implied lam, so do not be heedless.

It is only added with "an" (to), either explicitly or implicitly, not with a noun. This is because the fundamental form of the direct object is to be an explicit noun, so it is as if the lam were added as a compensation for departing from the fundamental form to that which replaces it—just as the sin is added in asta'a as a compensation for abandoning the root, which is ata'a. Although this addition is anomalous by analogy, its frequency in usage permits its employment in the Quran and eloquent speech. The same is said regarding its addition with the verb of will, such as aradtu li-an af'ala (I wanted to do). Al-Zamakhshari suggests that the reason for its addition there is that, since the verb contains the meaning of will, the lam is added to emphasize it. He also provides a rationale for its addition with the verb of command, especially since request and will belong to the same category.

Regarding the meaning, there are several interpretations:

1. That I be the first to submit in my time and among my people—that is, a submission in accordance with the command.
2. That I be the first of those whom I invited to Islam to submit.
3. That I be the first to invite himself to what he invited others to, so that I may be an example to be followed in both my speech and my actions, and so that my attribute may not be the attribute of kings who command what they do not do.
4. That I perform deeds of those who preceded me, which would render me worthy of primacy and honor—signifying the cause (the deeds through which honor is deserved) by the effect (the aforementioned primacy and honor in the majestic order).

Al-Zamakhshari mentioned this, but in al-Kashf, the preferred view among the four is the second, as it is the repeated and common interpretation in the Noble Quran. It encompasses all the other meanings, such as the agreement of speech with action and the necessity of the primacy of honor following from the primacy of foundation, whereas the other interpretations do not explicitly state that he was commanded to be the most honorable and the foremost. So understand this.