While some people were speaking about how the temple was adorned with costly stones and votive offerings, Jesus said,
"All that you see here--the days will come when there will not be left a stone upon another stone that will not be thrown down."
Then they asked him, "Teacher, when will this happen? And what sign will there be when all these things are about to happen?"
He answered, "See that you not be deceived, for many will come in my name, saying, 'I am he,' and 'The time has come.' Do not follow them!
When you hear of wars and insurrections, do not be terrified; for such things must happen first, but it will not immediately be the end."
Then he said to them, "Nation will rise against nation, and kingdom against kingdom.
There will be powerful earthquakes, famines, and plagues from place to place; and awesome sights and mighty signs will come from the sky."

Gospel commentary

Saint Cyril of Jerusalem (313-350), Bishop of Jerusalem, Doctor of the Church
Baptismal catechesis, no. 15

Our Lord Jesus Christ will come from heaven at the end of the world, on the last day. For the world will end and this created world will be renewed. For since corruption, theft, adultery and all kinds of sins cover the earth, and “bloodshed follows bloodshed over the land” (Hos 4:2), therefore this world will pass away and another, more lovely, will be established so that this wonderful dwelling place may not remain full of injustice. (…)

Hear what Isaiah says: “The heavens shall be rolled up like a scroll and the stars fall like the leaves of a fig tree” (cf. Is 34:4). And the Gospel also says: “The sun will be darkened and the moon will not give its light, and the stars will fall from the sky” (Mt 24:29). So let us not be dismayed as though we were the only ones who must die. The stars will also die and yet perhaps they will be brought to life again. The Lord will roll away the sky, not to destroy it but to restore it to life more lovely than before. Listen to the prophet David speaking: “Of old you established the earth, and the heavens are the work of your hands. They shall perish but you remain. They will all grow old like a garment; like clothing you change them and they will be changed” (Ps 102[101], 26-28). (…) Listen, too, to our Lord speaking: “Heaven and earth will pass away, but my words will not pass away” (Mt 24:35), for the authority of created things does not equal that of their Master's words.