1 Thessalonians 5:2

For yourselves know perfectly
With great exactness and accuracy, with great clearness and perspicuity, as a certain truth, which was made plain and evident to them, and about which there could be no question; and which perfect knowledge they had, either from the words of Christ, ( Matthew 24:42-44 ) , or from the ministration of the apostle and his fellow labourers, when among them:

that the day of the Lord;
of the Lord Jesus, when he will show himself to be King of kings, and Lord of lords, and the Judge of the whole earth; and which is sometimes styled the day of the Son of man, and the day of God, for Christ will appear then most gloriously, both in his divine and human nature; the day of redemption, that is, of the body from the grave, and from corruption and mortality; and the last day in which will be the resurrection of the dead, and the day of judgment, in which Christ will come to judge the quick and dead: and which

so cometh as a thief in the night;
at an unawares, and the Lord himself in that day will so come, ( Revelation 3:3 ) ( 16:1 ) respect is had not to the character of the thief, nor to the end of his coming; but to the manner of it, in the dark, indiscernibly, suddenly, and when not thought of and looked for; and such will be the coming of Christ, it will be sudden, and unknown before hand, and when least thought of and expected: and since the Thessalonians knew this full well, it was needless for the apostle to write about the time and season of it; which they were sensible of, could no more be known and fixed, than the coming of a thief into anyone of their houses.