Verse 31. - Heaven and earth shall pass away: but my words shall not pass away. Here is a distinct prediction that the present structure of the universe will pass away; that is, that it will be changed, that it will perish, as far as its present state and condition are concerned; but only that it may be refashioned in a more beautiful form. "We look for new heavens and a new earth, wherein dwelleth righteousness" (2 Peter 3:13). With this declaration of our blessed Lord all the discoveries of science coincide. Astronomy and geology alike concur in the conclusion that the whole system of the universe is moving onwards to its change. Our blessed Lord did but affirm that which is demonstrated by science. But my words shall not pass away; not merely the words which with his full self-consciousness he had just uttered respecting Jerusalem, but all his other words - all the revelation of God, all the words of him who is the Truth.

13:28-37 We have the application of this prophetic sermon. As to the destruction of Jerusalem, expect it to come very shortly. As to the end of the world, do not inquire when it will come, for of that day and that hour knoweth no man. Christ, as God, could not be ignorant of anything; but the Divine wisdom which dwelt in our Saviour, communicated itself to his human soul according to the Divine pleasure. As to both, our duty is to watch and pray. Our Lord Jesus, when he ascended on high, left something for all his servants to do. We ought to be always upon our watch, in expectation of his return. This applies to Christ's coming to us at our death, as well as to the general judgment. We know not whether our Master will come in the days of youth, or middle age, or old age; but, as soon as we are born, we begin to die, and therefore we must expect death. Our great care must be, that, whenever our Lord comes, he may not find us secure, indulging in ease and sloth, mindless of our work and duty. He says to all, Watch, that you may be found in peace, without spot, and blameless.Heaven and earth shall pass away,.... Which may be understood either affirmatively, as what will be at the second coming of Christ; or comparatively, rather than any thing said by Christ should; and so shows the certainty and irreversibleness of his predictions, as it follows:

but my words shall not pass away; which is true of all the words of Christ he ever spake, and here particularly relates to those he had just delivered, concerning the calamities that should come upon the Jewish nation; See Gill on Matthew 24:35.