Heaven and earth ....

http://www.worldwithoutend.info/bbc/books/articles/demar-gary_pp_04.htm

 

I believe it is helpful to look at the context:

"32 “From the fig tree learn its lesson: as soon as its branch becomes tender and puts out its leaves, you know that summer is near.

33 So also, when you see all these things, you know that he is near, at the very gates.

34 Truly, I say to you, this generation will not pass away until all these things take place.

35 Heaven and earth will pass away, but my words will not pass away."

The fig tree is Israel. Or was Israel, national, Old Covenant Israel. The nation had come to the point of judgment just like the fig tree in an earler incident where Christ cursed it for not having fruit. That tree - as well as national Israel as a whole - had leaves, a profession of godliness. But it had no fruits of righteousness. So its place as a nation was taken from it and given to the nation of Christians, the Israel of God (which includes believing Jews and Gentiles).

Verse 34 clearly implies that this generation (the unbelieving Jews of that time) will pass away. But it will be after all those things take place.

"Heaven and earth" is another name for Israel of the Old Covenant. I am quite willing to elaborate on this further from th OT. They "pass away" in the intervening years between AD 30 and 70. But in that period there are two different ages concurrently active, one passing away, one growing brighter and brighter.

Physical Heaven and Earth does not pass away. That is not the point of the passage. What passes away is the Old Covenant, the Temple system - which could never create true righteousness - and the elements (stoicheia) of that system.

Although the Old Covenant passed away the words of Christ are always with us. They are still relevant and necessary for our salvation.