What is the meaning of Matthew 24:42-44?

42 Watch therefore: for ye know not what hour your Lord doth come. 43 But know this, that if the goodman of the house had known in what watch the thief would come, he would have watched, and would not have suffered his house to be broken up. 44 Therefore be ye also ready: for in such an hour as ye think not the Son of man cometh. (Matthew 24:42-44 KJV)

William Burkitt’s Commentary

Here we have the application made by our Saviour, of the foregoing doctrine concerning the certainty and suddenness of a future judgment. Watch therefore, always; not without intermission, but without giving over; that ye may be not only in an habitual but actual readiness for my appearance.

Learn hence, That it is the indispensable duty, and ought to be the indefatigable endeavour of every Christian, to stand upon his watch in a prepared readiness for Christ’s appearance, both for his coming to us, and for our going to him.

Watch always, for ye know not the hour when our Lord cometh!