Isaiah 65:17

If these promises were in part fulfilled when the Jews, after their return out of captivity, were settled in peace in their own land and brought as it were into a new world, yet they were to have their full accomplishment in the gospel church, militant first and at length triumphant. The Jerusalem that is from above is free and is the mother of us all. In the graces and comforts which believers have in and from Christ we are to look for this new heaven and new earth. It is in the gospel that old things have passed away and all things have become new, and by it that those who are in Christ are new creatures, Co2 5:17. It was a mighty and happy change that was described Isa 65:16, that the former troubles were forgotten; but here it rises much higher: even the former world shall be forgotten and shall no more come into mind. Those that were converted to the Christian faith were so transported with the comforts of it that all the comforts they were before acquainted with became as nothing to them; not only their foregoing griefs, but their foregoing joys, were lost and swallowed up in this. The glorified saints will therefore have forgotten this world, because they will be entirely taken up with the other: For, behold, I create new heavens and a new earth.

— Matthew Henry's Concise Commentary (public domain)

As Caleb inherited the same land which his feet trod on (Deu 1:36; Jos 14:9), so Messiah and His saints shall inherit the renovated earth which once they trod while defiled by the enemy (Isa 34:4; Isa 51:16; Isa 66:22; Eze 21:27; Psa 2:8; Psa 37:11; Pe2 3:13; Heb 12:26-28 Rev 21:1). not be remembered--See on Isa 65:16, note on "troubles"; the words here answer to "the former . . . forgotten," &c. The former sorrows of the earth, under the fall, shall be so far from recurring, that their very remembrance shall be obliterated by the many mercies I will bestow on the new earth (Rev. 21:4-27).

— Jamieson-Fausset-Brown Commentary (public domain)