Charles Spurgeon Commentary Matthew 24:42

"Watch therefore: for ye know not on what day your Lord cometh." — Matthew 24:42 (ASV)

This is the practical conclusion of the whole matter. That our Lord is coming is certain. That His coming may be at any moment is a matter of faith; and that we are ignorant of the time of His coming is a matter of fact:

Ye know not what hour your Lord doth come. Christ’s words are in the present tense. He does not say, “You do not know what hour your Lord will come,” but, what hour your Lord doth come, as if to keep us always expecting Him.

And so that we would not fail to heed His words, He puts the command in the plainest language: Watch therefore. The title that He uses gives additional force to the command to His disciples to watch, for it is our Lord who is coming quickly.

That he will come, is certain. That his coming may be at any moment, is equally sure; and, therefore, we ought to be always ready for his appearing.

The Lord make us to be so!