Matthew 24:35 Heaven and earth will pass away, but my words will never pass away.
What we may think of as heaven and earth will change; maybe not the physical substance but certainly the quality of them. All the bad qualities of earth will be taken away with the sin and evil that man has continued to inject into this planet.
On the other hand, God has made sure that His Words have been written down and they will never change. Yes man will try to change things but God has continued to make sure that the scriptures have remained intact throughout history and He will continue to do so.
God’s promises remain. God’s Words remain. God is, has always been and always will be unchangeable and our Rock.