29 And he told them a parable: "Look at the fig tree, and all the trees; 30 as soon as they come out in leaf, you see for yourselves and know that the summer is already near. 31 So also, when you see these things taking place, you know that the kingdom of God is near. 32 Truly, I say to you, this generation will not pass away till all has taken place. 33 Heaven and earth will pass away, but my words will not pass away.
A Daily Quote from the early church fathers:
My words will not pass away, by an anonymous early author from the early Greek fathers
"'This generation' refers both to those who suffer temptation and to those who cause it. It refers to sinners among men and to the demons who are at work in them. For neither group will cease being in the world until its consummation. For Christ said, 'Depart from me, you cursed, into the eternal fire prepared for the devil and his angels' (Matthew 25:41). Moreover, it is necessary that the source of temptation be preserved as long as there is faith which needs testing. It is also possible, however, that 'this generation' refers to those mortal Christians who would not pass over into eternal life and be made immortal and impassible 'until' all the events about which Christ was speaking had taken place.
"'Heaven and earth will pass away, but my words will not pass away' because heaven and earth were created to serve you, but my words were uttered to govern you. Both heaven and earth are subject to vanity, as the apostle said, 'Creation is subject to vanity' (Romans 8:20). Truth, however, is by nature unable to deceive and can never die." (excerpt from INCOMPLETE WORK ON MATTHEW, HOMILY 49, the Greek fathers).