What a devout prayer this is, and what blessedness is intended in the discovery. Observe what the object of the petition is; not to know the hour of death, or the place of departure, or the means God in wisdom might appoint to produce the termination of life; these were not the subjects the Psalmist had in view; but that grace might so impress his mind with a sense of the frailty of life's tenure, that an habitual preparation, like a pilgrim on his journey, might make him always ready for the call. How sweetly and affectionately Jesus enforceth this, when he saith, Be ye also ready, for in such an hour as ye think not the Son of man cometh. Matthew 24:44.
Related Commentaries of Psalms 39:4
Psalms 39:4-5
4 LORD, make me to know mine end, and the measure of my days, what it is; that I may know how frail I am.
5 Behold, thou hast made my days as an handbreadth; and mine age is as nothing before thee: verily every man at his best state is altogether vanity. Selah.