1-thessalonians 5:2

For yourselves know perfectly - That is, they had been fully taught this. There could be no doubt in their minds respecting it.

The day of the Lord so cometh - Of the Lord Jesus - for so the word "Lord" in the New Testament commonly means; see the notes, Acts 1:24. The "day of the Lord" means that day in which he will be manifested, or in which he will be the prominent object in view of the assembled universe.

As a thief in the night - Suddenly and unexpectedly, as a robber breaks into a dwelling. A thief comes without giving any warning, or any indications of his approach. He not only gives none, but he is careful that none shall be given. It is a point with him that, if possible, the man whose house he is about to rob shall have no means of ascertaining his approach until he comes suddenly upon him; compare Matthew 24:37-43 notes; Luke 12:39-40 notes. In this way the Lord Jesus will return to judgment; and this proves that all the attempts to determine the day, the year, or the century when he will come, must be fallacious. He intends that his coming to this world shall be sudden and unexpected, "like that of a thief in the night;" that there shall be no such indications of his approach that it shall not be sudden and unexpected; and that no warning of it shall be given so that people may know the time of his appearing. If this be not the point of the comparison in expressions like this, what is it? Is there anything else in which his coming will resemble that of a thief? And if this be the true point of comparison, how can it be true that people can ascertain when that is to occur? Assuredly, if they can, his coming will not be like that of a thief; comp. notes on Acts 1:7.

5:2 For this in general ye do know; and ye can and need know no more.