Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Whether We let thee see something of that which We have promised them) of torment during your lifetime, (or make thee die (before its happening), thine is but conveyance (of the message)) on behalf of Allah, (Ours the reckoning) reward and punishment.
And whether ([read as] immā: the nūn of the conditional particle in, ‘whether’, has been assimiliated with the extra mā) We show you a part of that which We promise them, of chastisement, during your lifetime (the response of the conditional statement has been omitted, in other words [understand it as being], fa-dhāk [‘then so shall it be’]); or We take you [to Us], before chastising them; it is for you only to convey [the Message], your duty is only to deliver [the Message], and it is for Us to do the reckoning, when they finally come to Us, whereupon We shall requite them.
(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."