Ezra 1:1

"In the first year of Cyrus king of Persia, in order to fulfill the word of the Lord spoken by Jeremiah, the Lord moved the heart of Cyrus king of Persia to make a proclamation throughout his realm and to put it in writing:" NIV translation

This book is a historical book and, at this time, God's people were in captivity. The prophet Jeremiah had spent years and many tears warning the people that, if they did not repent, they would be taken into captivity. He also told them that their captivity would last seventy years and that is what this verse refers to. They did not repent and so God's presence left the temple and it was destroyed with the people taken into captivity. We see that God has opened the door for the people to return to Jerusalem by speaking to the heart of King Cyrus.

Ezra 1:2 - 4

"'This is what Cyrus king of Persia says: "The Lord, the God of heaven, has given me all the kingdoms of the earth and he has appointed me to build a temple for him at Jerusalem in Judah. Anyone of his people among you - may his God be with him, and let him go up to Jerusalem in Judah and build the temple of the Lord, the God of Israel, the God who is in Jerusalem. And the people of any place where survivors may now be living are to provide him with silver and gold, with goods and livestock, and with freewill offerings for the temple of God in Jerusalem."'" NIV translation

During this time, King Cyrus had come to know of God through the prophet Daniel. The phrase "God of heaven" began in the book of Daniel. We see, in his proclamation, the authority that the king has to open the door for their return and the fact that he did not compel the people to go but instead gave them the opportunity. 

This is a picture of how Jesus opened the doors of heaven to give us the opportunity to go there to be with Him. We also see that all of God's people were required to provide the materials to build the temple. This is a picture of God's desire for all Christians to work together to bring people into His kingdom.