The Book of Ezra records two major Jewish returns to the Promised Land from Babylon.
The first of these took place in 537 B.C. under the leadership of Sheshbazzar and then Zerubbabel. About 50,000 Jews returned, rebuilt the temple, and re-established worship as the Mosaic Law directed (chapters 1-6).
The second return occurred in 458 B.C. under Ezra's leadership. About 1,700 men, or 5,000 Jews, returned on that occasion, and the result was a restoration of the people's allegiance to the Mosaic Law. Their purified marriages illustrate the sincerity of their commitment.
In both returns God's sovereign control over the Persian kings is very evident. God moved the hearts of these men to permit His people to return and so fulfill His will (cf. Prov. 21:1). God can and will do seemingly impossible things to remain faithful to His Word.
This book is also a powerful revelation of how God deals with His chosen ones when they prove unfaithful to Him. He does not discard what He has chosen, but He fashions it anew when it fails.
