God has a PR problem.
As God's chosen people, Israel was to represent to the world the God who delivered them from slavery. Instead of revealing himself to all people, God had chosen to reveal himself specifically to one group of people, one nation, Israel. In turn, the Israelites were supposed to be a kingdom of priests, a holy nation, revealing God to all the other peoples of the earth through the holy, distinctive way of life to which God had called them. Israel was, in essence, God's public relations team.
However, one of the major themes of the book of Ezekiel is how badly the people of Israel failed in this PR task. God's chosen people have badly misrepresented Yahweh to the nations with their syncretism and idolatry which is so severe that Ezekiel describes his own people as a prostitute who gives herself out to everyone but her husband. As a result, God's name has been profaned among the nations. Instead of Israel bringing honor and glory to Yahweh, they have tarnished God's reputation, bringing shame upon the name of the God that they serve.
Anyone else who found themselves in this position would simply find new representation. Any celebrity or politician would quickly fire their agent or campaign manager if they couldn't do any better than this. And, in a way, that is what God does too... for a time. God does allow Israel to be taken into exile because of their unfaithful representation of him. Israel has to know that God will not tolerate his name being dragged through the mud in this way. But even this is only for a time.
In Ezekiel 36, God promises to bring back the people who have misrepresented him so badly. However, God makes abundantly clear in this passage that he is not doing this for their sake but for his own. Having failed so badly at their task, there is nothing that Israel could do to deserve God hiring them as his representatives once again. There is nothing that Israel can offer God. Instead, God says that he will deliver his people once again so that God himself will be honored and vindicated, so that his holiness will be known. God is doing this so that all the nations will know that God does not abandon his people and that God is powerful enough to save, even more powerful than the mightiest nations on earth.
However, God also will not allow these people to represent him as they are. He will not deliver them back into their old land which he gave them just so that they can go back to their old prostituting ways. No, God promises to cleanse his people and make them holy (even though they have not asked God to do this, of course, how could such an unholy people make such a holy request in the first place). God even says that he will perform a heart transplant, replacing their heart of stone with a heart of flesh. God is going to give this people his own Spirit so they will follow his Law and live the life God had always called them to live. This is the only way for the perpetual cycle of sin to be broken; to have God's own Spirit at work within us.
As Christians, we believe that this promise has been fulfilled in the person of Jesus Christ. We believe that the Spirit of God resided in Jesus, empowering his life and ministry, and that this same Spirit was poured out upon his followers, the Church, the New Israel. We believe that even though God knows our often whorish ways, he continues to call human beings to be his representatives in the world. God calls us to be made clean and to allow his Spirit to work in us so that we might truly represent him in all of his holiness.
Of course, we also know that all too often God still has a PR problem today. So many people claim the title "Christian" and by doing so claim to represent God in their thoughts, words, and deeds. But somehow none of those thoughts, words, or actions seem to look much like Jesus and so God's name ends up being dragged through the mud once again. Perhaps at the root of all this is our forgetting that what God does in us is not primarily about us but about God. We shouldn't think for a minute that this is for our sake, for our happiness, for our own self-fulfillment. After all Jesus taught that our first request in any prayer is for God's reputation to be honored; "Our Father who art in heaven, hallowed be thy name...". We have been called to honor God in all that we do and it is for that task that God says he will make us clean, give is a new heart, and place his very own Spirit within us.