John Calvin Commentary Matthew 24:42

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

Watch therefore. In Luke, the exhortation is more pointed, or at least more special: Take heed to yourselves, lest at any time your hearts be overcharged with surfeiting, and drunkenness, and the cares of this life. And certainly, he who, by living in intemperance, has his senses overloaded with food and wine, will never elevate his mind to meditation on the heavenly life. But as there is no desire of the flesh that does not intoxicate a man, they should take care, in all these respects, not to satiate themselves with the world, if they wish to advance with speed to the kingdom of Christ. The single word watch—which we find in Matthew—denotes that uninterrupted attention which keeps our minds in full activity, and makes us pass through the world like pilgrims.

In the account given by Mark, the disciples are first instructed to take heed lest, through carelessness or indolence, ruin overtake them; and next are commanded to watch, because various allurements of the flesh are continually creeping upon us, and lulling our minds to sleep.

Next follows an exhortation to prayer, because it is necessary to seek elsewhere the supplies that are necessary for supporting our weakness. Luke dictates the very form of prayer: first, that God may be pleased to rescue us from so deep and intricate a labyrinth, and next, that he may present us safe and sound in the presence of his Son—for we will never be able to reach it except by miraculously escaping innumerable deaths.

And as it was not enough to pass through the course of the present life by overcoming all dangers, Christ places this as the most important: that we may be permitted to stand before his tribunal.

For you know not at what hour your Lord will come. It should be observed that the uncertainty about the time of Christ’s coming—which almost all treat as an encouragement to laziness—should, for us, be an incitement to attention and watchfulness. God intended that it should be hidden from us for the express purpose that we may keep diligent watch without relaxing for a single hour. For what would be the trial of faith and patience if believers, after spending their whole life in ease, laziness, and pleasure, were to prepare themselves in just three days for meeting Christ?