Though the book of Ezra appears relatively early in your Bible, it represents events that happen at the very tail end of recorded Old Testament history. What happens in Ezra, and the companion volume, Nehemiah, happen 400-500 years before the birth of Christ, so there is a lot of history and theology that gets focused in this book that then leads us straight to the New Testament and God's plan in Christ.
To begin with, God's people are captives in Babylon when Cyrus the king of the Persians defeats the Babylonians. Some of God's people have been in captivity for almost 200 years, and others only for a few decades. But because of their rebellion, the land has sat nearly empty for a long time. After the fires of conquest, the dust has settled, the embers have grown cold, and a long dark night has settled in on the Promised Land. But as Ezra opens, the light of dawn begins to crack over the horizon.
Cyrus decided it was time to send God's people home with plenty of wealth to rebuild the Temple. But this isn't just the kindness of a benevolent dictator. God stirred his heart. God laid out this plan since the days of Jeremiah the prophet, and even earlier. Through Isaiah the prophet, God called Cyrus by name and laid out what he was going to do for his people, temple, and city nearly 200 years before he was born. Then, decades before Cyrus defeats the Babylonians, God says through Jeremiah that he is going to send his exiled people home. In fact, this is the context of the most well known passage in Jeremiah,
"For I know the plans I have for you, declares the Lord, plans for wholeness and not for evil, to give you a future and a home. Then you will call upon me and some and pray to me, and I will hear you" (Jeremiah 29:11-12).
When God tells his people this, they are powerless captives in a foreign and pagan land. Just before Ezra 1:1 opens, God's people have been given the promise that they will return home, but they have absolutely no earthly power to make that happen. If they do go home, it will have to be because someone more powerful than they are makes it happen. And so it does,
"In the first year of Cyrus king of Persia, that the word of the Lord by the mouth of Jeremiah might be fulfilled, the Lord stirred up the spirit of Cyrus" (Ezra 1:1).
Something incredible is true for the follower of Jesus Christ - you can be utterly powerless in this world and still have good reason for hope. God's people were powerless captives, but got to go home anyway. They did not have what we would call economic leverage, but they went home loaded to the gills with Persian treasure and all the valuables plundered from the temple a generation before. And it all happened because God performed it and showed faithful love to broken and enslaved people.
God rebuilds his people. God has every desire to fill his children's life with his. God is powerful enough to not be put on his heels by any complication or disadvantage we have. God's promise to the exiles in Babylon belongs to all his children, but note what the promise is. It is that he will gather us in his presence, we will seek him, we will find him, we will pray to him, and he will hear us.
This is the promise given in our darkness and is the light of God dawning in our lives.