Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(See they not) i.e. the people of Mecca (how We visit the land) how We seize the land, (reducing it of) opening it up to Muhammad (pbuh) from (its outlying parts?) from its surrounding sides; it is also said that this refers to the death of the men of knowledge. ((When) Allah doometh) when He decrees the conquest of cities or the death of scholars (there is none that can postpone) there is nothing that can change this. (His doom, and He is swift at reckoning) His torment is severe; it is also said that this means: when He takes people to task, His reckoning is severe.
Or is it that they, the people of Mecca, have not seen how We visit the land, [how] We target their land, diminishing it at its outlying regions?, by giving victory to the Prophet (s). And God judges, among His creatures as He will; there is none that can repel His judgement and He is swift at reckoning.
Or is it that they have not seen how We visit the land, We seek out the land of the body at the moment of old age, diminishing it at its edgesḍ, by the [gradual] wearing away of its organs, the failure of its faculties and the weakening of its senses bit by bit until death. And God judges, in this way; there is none that can repel His judgement, none to avert or change His judgement. Or [it means that] We visit the land of the soul at the moment of wayfaring, diminishing it at its edges by annihilating its acts with Our acts first, as He has said, 'Through Me he hears and through Me he sees', then, second, by annihilating its attributes with Our attributes, as He has said, '[Until] I am his hearing with which he hears and his sight by which he sees', then by annihilating its essence by Our essence, as He has said to whom does Sovereignty belong on this dayḍ [Q. 40:16], responding Himself with His words To God, the One, the Vanquisher [Q. 40:16], since creation in its entirety will have been annihilated; thereupon there will be only God's judgement, judging as He will without any to repel His judgement since anything other than Him does not exist.
(So remind them - you are only one who reminds. You are not a dictator over them - Save the one who turns away and disbelieves. Then Allah will punish him with the greatest punishment. Verily, to Us will be their return, Then verily, for Us will be their reckoning.)88:21-26 Allah said next,
(See they not that We gradually reduce the land from its outlying borders.) Ibn `Abbas commented, "See they not that We are granting land after land to Muhammad '' Al-Hasan and Ad-Dahhak commented that this Ayah refers to Muslims gaining the upper hand over idolators, just as Allah said in another Ayah,
(And indeed We have destroyed towns round about you.) 46:27
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
This is to console the Holy Prophet, as if to say, "O Prophet, you need not concern yourself as to the end of these disbelievers who have rejected the Truth. You should go on performing with peace of mind the Mission that has been entrusted to you and leave it to Us to give them suitable punishment." Though this has been addressed to the Holy Prophet, it is obvious that it is really meant to warn the opponents of the Truth, who were demanding definitely from the Holy Prophet by way of a challenge to bring about the scourge about which threats were being held out to them.
"We are advancing in the land"= this is a very subtle way of warning the opponents of the Truth: "The fact that Our Message is spreading fast in Arabia does, in fact, mean that We Ourselves are advancing very fast in the country against you for We are with those who are carrying Our Message."
"We are shrinking its boundaries for them"= "We are causing the influence of Islam to spread fast in the land and are thus reducing the boundaries of the influence of its opponents. Are not these things the portents of their coming disaster?"
That is, "These people, who are now devising schemes to defeat the Message of the Truth, do not take a lesson from the sad end of the people who devised similar schemes before them to suppress the voice of the Truth by falsehood, fraud and persecution."