John Gill Commentary 1 Thessalonians 4:15

"For this we say unto you by the word of the Lord, that we that are alive, that are left unto the coming of the Lord, shall in no wise precede them that are fallen asleep." — 1 Thessalonians 4:15 (ASV)

For this we say to you by the word of the Lord
The apostle, delivering something new and extraordinary concerning the coming of Christ, the first resurrection (or the resurrection of the saints), the change of the living saints, and the rapture both of the raised and living in the clouds to meet Christ in the air, expresses himself in this manner.

This is either in allusion to the prophets of old, to whom the word of the Lord is said to come, and who usually introduced their prophecies with a "Thus says the Lord"; or in distinction from his own private sense, sentiment, and opinion of things.

He is signifying that what he was about to say was not a fancy and conjecture of his own, the fruit and produce of his own brain, but what he could assert upon a sure foundation, upon the best and greatest authority, even the word of the Lord.

This has respect either to some particular word of Christ, as some think, such as (Matthew 24:30Matthew 24:31) (John 5:28John 5:29), or rather to a particular and peculiar revelation and special instruction in these things he had immediately from Christ.

And it may be when he was caught up into the third heaven himself, and had an experience in himself of somewhat of that which both the living and raised saints shall feel when they are caught up together in the clouds, since the change of the living saints at the time of the resurrection of the dead is a mystery which seems to have been first made known to and discovered by the Apostle Paul; see (1 Corinthians 15:51 1 Corinthians 15:52).

That we who are alive, and remain until the coming of the Lord :
Not that the apostle thought that he and the saints then in the flesh should live and continue until the second coming of Christ; for he did not imagine that the coming of Christ was so near, as is manifest from (2 Thessalonians 2:1–3), though the Thessalonians might take him in this sense, which he there corrects.

But he speaks of himself and others in the first person plural, by way of instance and example, for illustration's sake; that supposing he and others should be then in being, the following would be the case.

And moreover, he might use such a way of speaking with great propriety of other saints, and even of those unborn, and that will be on the spot when Christ will come a second time, since all the saints make up one body, one family, one church and general assembly; so that the apostle might truly and justly say, "we who are alive"; that is, as many of our body, of our family, of our church or society, that will be living at the coming of Christ.

And he might choose the rather to speak in this form, person, and tense, to awaken the care, circumspection, diligence, and watchfulness of the saints, since it could not be known how soon the Lord would come.

However, from hence it appears that there will be saints alive at Christ's second coming; he will have a seed to serve him until he comes again; he always has had in the worst of times, and will have, and that even in the last days, in the days of the son of man, which are said to be like those of Noah and of Lot.

And these are said to "remain," or to be "left"; these will be a remnant, the residue and remainder of the election of grace, and will be such as have escaped the fury of antichrist and his followers, or of the persecutors of the saints.

Now these

will not prevent them who are asleep :
That is, who are dead, so the Ethiopic version; the reason why the dead are so called, see in the note on the preceding verses.

The sense is, either they "will not come up to them who are asleep, or dead," as the Syriac, Arabic, and Ethiopic versions render the words; they will not come into the state of the dead, they will undergo a change equivalent to death, but not death itself; see (1 Corinthians 15:51 1 Corinthians 15:52).

Or rather they "will not go before" them; they will not get the start of them, and be in the arms of Jesus, and enjoy his presence when he comes, before the dead in Christ, which might be thought, but this will not be the case.

For the dead saints will rise before the living ones are changed, and both will be caught up together to meet the Lord, as is said in the following verses; so that the one will not come or go before the other, or come at, or into the enjoyment of Christ first, but both together.