Tafsir of Al-A'la 87:10

He who fears will be reminded; meaning, he who is of the nature to fear Allah Almighty—with the true sense of fearing Him, or who fears Allah Almighty in a general sense—will be reminded by your admonition. Through this reminder, he will increase in fear, reflect upon the matter with which you admonish him, grasp its reality, and believe in it.

It is said that ‘in’ (if) here carries the meaning of ‘idh’ (since/when), as in His saying, “And you are the superior ones if you are believers” (3:139), meaning: since you are believers. This is because He, glory be to Him, did not inform them that they were the superior ones except after their belief. Similarly, there is the saying of the Prophet (may the blessings and peace of Allah be upon him) regarding the visitation of the graves: “And I, if (since) Allah wills, will join you.” The Kufans affirmed this meaning for the particle based on what has been mentioned and its parallels, while those who reject this have provided responses found in Al-Mughni and elsewhere.

It is also said that it carries the meaning of ‘qad’ (indeed), a meaning supported by Qutrub.

Isam al-Din al-Maridi stated that the admonition should be regarding what is of utmost importance to the one being admonished. Therefore, it is appropriate to remind disbelievers of faith—not of secondary branches like prayer, fasting, and pilgrimage—since these are of no benefit to them without faith. Likewise, it is appropriate to remind a believer who neglects prayer of the prayer specifically, rather than of faith, for example. Thus, it is as if it were said: Remind each person of what benefits him and is appropriate for him.

Al-Farra’, Al-Nahhas, Al-Jurjani, and Al-Zahrawi said the discourse is based on ‘al-iktifa’ (sufficiency/omission), and the original intended meaning is: "So remind, if the reminder benefits," and even if it does not benefit, as in His saying, “garments to protect you from the heat” (16:81) [implying also from the cold].

It is evident that those who do not subscribe to the "concept of opposition" (mafhum al-mukhalafah)—whether it be the concept of a conditional clause or otherwise—face no difficulty with this verse, as is not hidden.