[Matthew Henry’s Complete Commentary on the Whole Bible]. This is not designed for a command to the prophet, so much as for a threatening to the people, that they should have no benefit by the prayers of their friends for them.

[Jamieson Fausset Brown Bible Commentary, 1871]. There is a climax of guilt which admits of no further intercessory prayer (Ex 32:10, in the Chaldee version, "leave off praying"; Jer 7:16; 1Sa 16:1; 15:35; 1Jo 5:16). Our mind should be at one with God in all that He is doing, even in the rejection of the reprobate.

[The People’s New Testament]. It seems that the Thessalonian brethren, expecting the speedy coming of the Lord, mourned over some of their number who had died, counting it a great loss that they did not live to meet Jesus. What we call death is only falling asleep in the arms of our Lord.

[Barnes’ New Testament Notes]. [I]t would appear that they supposed that those who had died, though they were true Christians, would be deprived of some important advantages which those would possess who should survive to the coming of the Lord. There seems some reason to suppose (1) that some among them doubted whether there would be any resurrection, (comp. 1 Cor. xv. 12, ) and (2) that they supposed that they who had died were thus cut off from the hope of eternal happiness, so as to leave their surviving friends to sorrow “as those who had no hope.”

[Adam Clarke’s 1810/1825 commentary and critical notes on the Bible]. It is supposed that the apostle had heard that the Thessalonians continued to lament over their dead, as the heathens did in general who had no hope of the resurrection of the body; and that they had been puzzled concerning the doctrine of the resurrection. To set them right on this important subject, he delivers three important truths: 1. He asserts, as he had done before, that they who died in the Lord should have, in virtue of Christ’s resurrection, a resurrection unto eternal life and blessedness. 2. He makes a new discovery, that the last generation should not die at all, but be in a moment changed to immortals. 3. He adds another new discovery, that, though the living should not die, but be transformed, yet the dead should first be raised, and be made glorious and immortal; and so, in some measure, have the preference and advantage of such as shall then be found alive.