Tafsir of Fussilat 41:31

(We are your allies in the worldly life)—this is among their glad tidings in this world—meaning: we are your helpers in your affairs, inspiring you toward the truth and guiding you to that which contains your goodness and righteousness. It may be that this refers to what occurs to the minds of believers who persist in acts of obedience: that this is by the success granted by Allah the Exalted and His support for them through the agency of the angels, peace be upon them.

It is permissible, according to the view of some, that the angels say to some of the righteous—orally, in contexts other than those [specific] occasions—: "We are your allies in the worldly life and in the Hereafter." We aid you with intercession and receive you with honor when, between the disbelievers and their companions, there occurs what occurs of claims and disputes.

Some exegetes have held that this is also among their glad tidings in one of the three instances [of their descent], with the meaning: "We were your allies in the world, and we are your allies in the Hereafter." It is also said: This is the speech of Allah the Exalted, not the angels, meaning: We are your allies through guidance and sufficiency in the world and the Hereafter.

(And for you therein)—that is, in the Hereafter—(is whatever your souls desire) of various kinds of pleasures.

(And for you therein is whatever you request)—meaning: whatever you wish for. It is a derivative of al-du'a (calling/supplication) in the sense of requesting, meaning: whatever you claim for yourselves. According to some, it is more general than the first, because a request may occur regarding abstract matters and intellectual or spiritual virtues. It is said: There is a particular and general relationship between the two from one perspective, since a person may desire that which he does not request—like a sick person who desires that which harms him but does not seek it. The claim that tamanni (wishing/hoping) is more general than irada (will/desire) is not accepted. Yes, it is said: If by tamanni one intends what is valid to be wished for, rather than what is actually wished for, then that is [different].

Ibn 'Isa said: The meaning is "whatever you claim is yours, it shall be yours by the judgment of your Lord."

"For you" in both instances is a predicate, and "what" is the subject. "Therein" is a circumstantial qualifier pertaining to the pronoun within the predicate. The lack of sufficiency in merely conjoining "what you request" to "what you desire" is to indicate the independence of each one.