This is a good question, full of good things to consider. First, read two scriptures: (1) “…the earth abides forever;” (Ecclesiastes 1:4) and (2) “For Christ has entered, . . . into heaven itself, now to appear in the presence of God on our behalf.” (Hebrews 9:24 ESV) These verses establish that heaven and earth are physical places where beings dwell, and that both places will exist forever.

What then is meant by the expression, “Heaven and earth shall pass away: but my words shall not pass away,” in Mark 13:31 and in Matthew 24:35? This concept is also referenced in 2 Peter 3 where Peter wrote about two different sets of heavens and earths. One set was in the time of the great flood and the second set in our present time. Here the word heavens symbolize the higher or spiritual controlling powers, and earth symbolizes human government and social arrangements

Thus, the first heavens and earth, or the order and arrangement of things then existing, having served their purpose, ended at the flood. But the physical heavens (sky and atmosphere), and the physical earth, did not pass away; they remained. So likewise, the present world (heavens and earth) will pass away with a great noise, fire and melting—confusion, trouble, and dissolution. The present order or arrangement of government and society, not that of the physical sky and earth, will pass away

The present heavens (powers of spiritual control) must give place to the “new heavens”—Christ's spiritual control. The present earth must (symbolically) melt and be dissolved, in the beginning of the “Day of the Lord,” which “shall burn as an oven.” (Malachi 4:1) It will be succeeded by “a new earth,” i.e., society reorganized in harmony with earth’s new King—Christ. It will be organized or based on love and justice, rather than on might and oppression. This is the Kingdom for which we pray, “Thy Kingdom come, thy will be done on earth as it is in heaven.” 

In summary, the text “Heaven and earth shall pass away: but my words shall not pass away,” indicates that earth’s government and controls of the present time will not exist anymore.  God’s Kingdom will take its place. 2 Peter 3:13 (NIV), “But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells.” This new heaven and new earth will NEVER pass away!

“In the days of those kings, the God of the heavens will set up a kingdom that will never be destroyed,… It will crush all these kingdoms and bring them to an end, but will itself endure forever.” Daniel 2:44 (CSB)