Here's what I see, let me know how you might differ If you dislike long posts, then this is going to be upsetting -- it's long. Please feel free to critique.
17 For, behold, I create new heavens and new earth. And the former things shall not be recalled, and they shall not go up on the heart.
This very verse is referenced as a promise in 2Pe 3:13 "But according to His promise, we look for "new heavens and a new earth," in which righteousness dwells". 2Peter 3 is in the context of the return of Christ, "looking for hastening the coming of the Day of God, through which the heavens having been set afire will be dissolved; and burning, the elements will melt", which means Isaiah 65 is dealing with the same timeframe.
The new heavens and new earth follow the destruction of the wicked seen in Rev 20:15 And if anyone was not found having been written in the Book of Life, he was thrown into the Lake of Fire. The next event John sees is Rev 21:1, "And I saw a new heaven and a new earth, for the first heaven and the first earth passed away, and the sea no longer is". We can be confident then Isaiah 65 is dealing with these events and is not allegorical (as a symbol relating to the establishment of Christ's Kingdom). Revelation 21:4, "death shall be no longer, nor mourning, nor outcry, nor will there be pain any more; for the first things passed away" replies to Isaiah 65:17 "...And the former things shall not be recalled, and they shall not go up on the heart
18 However, be glad and rejoice forever in what I create. For, behold, I create in Jerusalem a rejoicing, and her people a joy.
This Jerusalem is one in the same as the bride prepared for her Husband in Rev 21:2, "And I, John, saw the holy city, New Jerusalem, coming down out of Heaven from God, having been prepared as a bride, having been adorned for her Husband". The elect are created anew in Christ with joy, the true Church, becoming as it were God's Jerusalem; rejoicing in what God has done. (Heb 12:22)
19 And I will rejoice in Jerusalem, and joy in My people. And the voice of weeping and the voice of crying shall no longer be heard in her.
God rejoices in His bride, the elect, whom He has prepared for Himself to dwell amongst and be their God everlastingly. As Ezekiel speaks of this, God dwells (tabernacles) with men: Ezekiel 37:27-28, "And My tabernacle shall be with them, and I will be their God, and they shall be My people. And when My sanctuary shall be in their midst forever, the nations shall know that I, Jehovah, sanctify Israel". God will reside with His elect, being their God and we His people, forever. Revelation says no different:
Rev 21:3 And I heard a loud voice out of heaven, saying, "Look! The tabernacle of God [is] with the people, and He will tabernacle [or, dwell] with them. And they will be His people, and God Himself will be with them.
Now comes a seemingly difficult verse, especially for those who reason a literal millennium will ensue where people will experience life-extension as Christ rules from a literal Jerusalem. However, we have the context: The new heavens follows Judgment Day and the destruction of the earth with fire; Isaiah 65 cannot be taken literally, without violating Scripture -- though some are willing to do so to keep their earthly reign.
20 Neither shall there be there any more an infant of days, or an old man who shall not complete his time: for the youth shall be a hundred years old, and the sinner who dies at a hundred years shall also be accursed.
Revelation 21:4 says clearly that in the new heaven and earth "And death shall be no longer", which seems problematic considering verse 20 says "the youth shall die the son of a hundered years". So, which is it? The answer, I believe, is that God is using an analogy of lifespan to prove a spiritual point.
There "shall no more be an infant" that dies with only short days to its credit or an old man who will not complete his appointed span. Logically, if an infant doesn't die young, it becomes an old man, and old men die only when there time is full, thereby ensuring all to live until the fullness of their time. Yet, this is speaking of the new heavens, there is no death, there is no marriage, there are no children or old men. We have been raised and changed, the corruptible putting on incorruptible, 1Co 15:53 "For this corruptible must put on incorruption, and this mortal must put on immortality."
The solution is in the fullness of our time in heaven. The fullness of our time is 100, signifying a complete life (10 being completeness), something we cannot reach. We never reach that span where we have completed our time. "For a child shall die a hundred years old", if that were possible to fully complete (100) our life in the new heavens and earth, which it is not. Just as Rev 22:5 states of that time, "And they shall reign to the ages of the ages", we shall never fulfill the circuit of our days, it is an everlasting existence.
However, for the sinner, he remains dead until the fullness of time (hundred years), and shall remain accursed, "and the sinner who dies at a hundred years shall also be accursed". Rev 22:15 is clear the wicked continue in the second death, Rev 22:15 "But outside are the dogs and the sorcerers, and the fornicators, and the murderers, and the idolaters, and everyone loving a lie, and making it". Even unto the completeness of days (never ending), the wicked remain accursed; a fearful, never ending torment for those outside God.
21-22 And they shall build houses and live in them; and they shall plant vineyards and eat their fruit. They shall not build, and another live in them; they shall not plant, and another eat.
The building of houses and planting vineyards implies the elect will dwell in the land for a long time. We see similar instructions during the Babylonian captivity: Jer 29:28 "On account of this he sent to us in Babylon, saying, This exile is long; build houses and live; and plant gardens and eat their fruit". In this world we are strangers and pilgrims (see Jer 35:7 where Jonadab remained a pilgrim refusing to build or plant), but in the new heavens we are established forever. This same truth is found in Ezekiel 28:25-26, where God promises to one day have Spiritual Israel dwell securely in the land (heaven) and build houses and plant vineyards.
So says the Lord Jehovah: When I have gathered the house of Israel from the peoples among whom they are dispersed, and have been sanctified in them in the sight of the nations, then they shall dwell on their land which I have given to My servant Jacob. And they shall dwell in it securely and shall build houses and plant vineyards. Yes, they shall dwell securely, when I have done judgments on all those who hate them round about them. And they shall know that I am Jehovah their God.
Isaiah 65:23 "For like the days of the tree are the days of My people; and My elect shall grow old to the work of their hands. They shall not labor in vain, nor bring forth for terror. For they are the seed of the beloved ones of Jehovah, and their offspring with them".
What are the days of a tree? Rather long, or as Psalm 52 says "everlasting", Psa 52:8 "But I am like a green olive tree in the house of God; I trust in the mercy of God forever and ever." Those under the covenant of God are trees, some will endure, while others never had Root and will be destroyed:
Isaiah 1:30-31 "For you shall be like a tree whose leaf fades, and like a garden that has no water in it. And the strong one shall be for tow, and his work for a spark; and they shall burn both together; and no one shall quench them".
What is the meaning of "My elect will long enjoy the work of their hands"? In the new heaven, what is the work of the elect? Remembering 1 Corinthians 3:13-14, "...each one's work shall be revealed. For the Day shall declare it, because it shall be revealed by fire; and the fire shall try each one's work as to what kind it is. If anyone's work which he built remains, he shall receive a reward".
Our work is the reaping of souls through the preaching of the word; those that really passed through the fire with Christ will be a good kind, "not for terror (Judgment) or in vain", but our work that we built will remain )as God blesses). In this, because we have gathered some good wheat into the storehouse (God gives the increase), we will be able to enjoy the work of our hands (fellow believers) eternally with us.
This is as so much what the last of the verse says, "For they are the fruit of the blessed ones of Jehovah, and their produce with them". The elect are the fruit or seed of Jehovah's work, and the elect bring into heaven with them those (produce or offspring) they have toiled over. That the elect are the offspring of God is sure:
Acts 17:28-29 "For in Him we live and move and exist, as also some of the poets among you have said, For we are also His offspring. Then being offspring of God, we ought not to suppose that the Godhead is like gold or silver or stone, engraved by art and the imagination of man."
24 And it will be, before they call, I will answer. While they are speaking, then I will hear.
In verse 24 is the assurance from God that to His blessed ones, the offspring of God, He will answer in salvation before they call upon Him. God replies in salvation before the elect call, He hears will they are pleading God for salvation. This is a reminder of the true nature of salvation.
25 The wolf and the lamb shall feed as one; and the lion shall eat straw like the ox. And dust is the food of the snake. They shall not do evil nor destroy in all My holy mountain, says Jehovah.
Verse 25 ends our discussion of Isaiah 65. Should we think that the lamb and wolf are to be understood as real earthly wolves and lambs? Verse 25 is continuing the salvation of God to its conclusion. In the new heavens and earth, that which was started in us will be completed. It is speaking of God's covenant of peace wherein there is reconciliation between God and man (Hosea 2:18-19 And in that day I will cut a covenant for them with the beasts of the field, and with the birds of the heavens, and the creepers of the ground. And I will break the bow and the sword, and the battle out of the earth, and I will make them to lie down safely. And I will betroth you to Me forever. Yes, I will betroth you to Me in righteousness, and in judgment, and in mercy, and in compassions.
Those creatures that are at war will become at rest from their warfare, the wolf and the lamb will feed as one, both subject to God. This is the covenant of salvation that God makes, that we will be safe before God, though we were wild -- yet we are betrothed to God forever, who has compassion on us. Again, the remnant of Israel shall feed and lie down together in salvation:
Zephaniah 3:13-15, "The remnant of Israel shall not do injustice, nor speak lies. And a deceitful tongue shall not be found in their mouth. For they shall feed and lie down, and no one shall frighten them. Shout for joy, daughter of Zion; shout, Israel! Be glad and rejoice with all the heart, daughter of Jerusalem! Jehovah has turned off your judgments; He has turned away your enemy. Jehovah, the King of Israel, is in your midst; you shall not fear evil any more".
Lastly we have: "And dust is the food of the snake. They shall not do evil nor destroy in all My holy mountain, says Jehovah." That old snake Satan will be eating dirt, under God's wrath in the Lake of Fire, unable to cause any more trouble. Zion, God's Holy Mountain, the Kingdom the elect enter into upon salvation, is pure and undefiled. In this Kingdom the kings (elect) will walk: Rev 21:24 And the nations of the ones saved will walk in its light; and the kings of the earth bring their glory and honor into it. Though, salvation comes in our spirit so that we are at peace with God, it is not until this body of death is removed and we are clothed in our new heavenly body that we enter perfect peace in the presence of the Lamb.
Revelation 21:22-23 "And I saw no temple in it, for the Lord God Almighty is its temple, even the Lamb. And the city had no need of the sun, nor of the moon, that they might shine in it, for the glory of God illuminated it, even its lamp is the Lamb."
And so, the Kingdom of God, His Holy Mountain, Zion, is at peace -- all enmity ceased forever. Thus concludes the study of Isaiah 65, a study in the salvation of God.