Who was the author? According to tradition, Samuel may have been the person whom the Holy Spirit inspired to write the book of Ruth, or others may have written the book later during David's reign.
What is the book? The book of Ruth gives the account of the foreign woman by that name who by God's grace was an ancestress of King David and the Lord Jesus Christ.
Where was it written? As with Judges, if Samuel wrote Ruth he may have written it in Ramah, and, if Ruth was written later during David's reign, the book may have been written in Jerusalem.
When was it written? Again like Judges, Ruth may have been written before 1050 B.C., or it may have been written later, but probably no later than 970 B.C.
Why? The book likely was written at least in part to give some of the background of David's and Christ's line, but more significantly for us its story tells how God lovingly brings people of all nations into His kingdom by faith, through which He redeems them by Jesus's blood. The book of Ruth also gives what could be considered a more-positive spin than the book of Judges on that era (1375-1050 B.C.).
How? The book of Ruth is particularly noted for its compactness, vividness, warmth, beauty, and dramatic effectiveness. The book's narrative of Ruth and Boaz selflessly helping Naomi move from emptiness to fullness is symmetrical, with the crucial turning point precisely at its midpoint and with corresponding movements in space, time and circumstances resulting in a harmony that is artistically pleasing and edifyingly beneficial.
For further reading on the book of Ruth:
- Cundall, Arthur E. and Leon Morris. Judges & Ruth: An Introduction and Commentary, Tyndale Old Testament Commentaries, general editor D. J. Wiseman. Downers Grove, IL: Inter-Varsity Press, 1968. (I had this little volume in my library before I acquired the Keil-Delitzsch volume below, but I still consult it from time to time and generally find it more accessible and useful.)
- Wilch, John R. Ruth, Concordia Commentary: A Theological Exposition of Sacred Scripture. Saint Louis, Missouri: Concordia Publishing House, 2006. (I don't own this volume, but Dr. Wilch was one of my seminary professors and is quite knowledgeable. In general, I have found this series of commentaries to be both scholarly and accessible. You can see the catalog description for this volume on Ruth here.)