“For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.”
King James Version (KJV)
4:15 By the word of the Lord - By a particular revelation. We who are left - This intimates the fewness of those who will be then alive, compared to the multitude of the dead. Believers of all ages and nations make up, as it were, one body; in consideration of which, the believers of that age might put themselves in the place, and speak in the person, of them who were to live till the coming of the Lord. Not that St. Paul hereby asserted (though some seem to have imagined so) that the day of the Lord was at hand.
1Th 4:15 For this we say. He now explains how it will be the Lord's coming. We which are alive [and] remain. We who are on the earth when the Lord comes, will not precede those who died in the Lord to meet him.