Ezekiel 36 represents a dramatic switch in God's messages through His prophet. No longer is the word one of doom and gloom, invasion and exile. Instead, Ezekiel reveals that Israel is soon to be blessed with the return of the exiles and a repopulation of the Promised Land - but he takes pains to point out that this is not because of her own doing. It is the Lord's will out of concern for His name. Just as Israel's punishment was a sign of His holiness, her flowering will be a sign of His grace.
Here is God's good plan for His people: "But you, O mountains of Israel, shall shoot out your branches, and yield your fruit to my people Israel; for they shall soon come home. See now, I am for you; I will turn to you, and you shall be tilled and sown; and I will multiply your population, the whole house of Israel, all of it; the towns shall be inhabited and the waste places rebuilt; and I will multiply human beings and animals upon you. They shall increase and be fruitful; and I will cause you to be inhabited as in your former times, and will do more good to you than ever before. Then you shall know that I am the Lord" (vs. 8-11). God, who was previously against Judah, is now for her and will turn to her!
But lest Israel think that this is all due to her own goodness, Ezekiel makes clear that God is restoring the people to prove His covenant faithfulness: "It is not for your sake that I will act, says the Lord God; let that be known to you. Be ashamed and dismayed for your ways, O house of Israel...Then the nations that are left all around you shall know that I, the Lord, have rebuilt the ruined places, and replanted that which was desolate; I, the Lord, have spoken, and I will do it" (vs. 32 and 36). The restoration is going to happen more in spite of Israel's behavior than as a reward for it. Remember, the biblical story is more about the goodness of God than about the righteousness of humanity.
One side note - notice the profound New Testament foreshadowing in verses 25 through 27. We hear talk of "sprinkling clean water" (baptism?), being cleansed from uncleanness (forgiveness?), a new heart (regeneration/being born again as a new creation?) and a new spirit put within us (pouring out of the Holy Spirit on Pentecost?) These rumblings point to a brand new direction in God's story with His people. "I will sprinkle clean water upon you, and you shall be clean from all your uncleannesses, and from all your idols I will cleanse you. A new heart I will give you, and a new spirit I will put within you; and I will remove from your body the heart of stone and give you a heart of flesh. I will put my spirit within you, and make you follow my statutes and be careful to observe my ordinances." Certainly God is up to something big!