The book of Ruth connects the book of Judges with the books of Samuel. The first verse of the book points to the time of the Judges and the very last verse points to King David.
An author is not mentioned in Ruth. As the genealogy in chapter 4:17.22 goes down to King David this short book of Ruth was written at the time of David (around 1000 BC). According to the Babylonian Talmud of the Jews Samuel the prophet may have been the author of the book of Ruth. This view is shared by many Bible expositors.
The book of Ruth describes the grace of God.
Despite the sin and apostasy of the people of Israel during the times of the Judges Jehovah is fulfilling His promises in regard to the coming Messiah.
Ruth, the Moabitess, who as a heathen could not have any right amidst the people of God (according to the law) takes refuge with the God of Israel and is received into His people by His grace.
By her marriage with Boaz the redeemer (hebr. go’el) she receives a place in King David’s genealogy and by it also in the Messiah’s (Jesus of Nazareth) genealogy (Ruth 4:22; Matthew 1:5).
The main person of the book is Boaz the redeemer. His name is mentioned nearly twice as often as Ruth’s name! The redeemer played an important part in Israel and is a picture of Christ the redeemer.
Typically the book describes how God will receive the remnant of the people of Israel in the time of the end. Naomi typifies the people of Israel who have left their country and lost it all. Ruth is a picture of the remnant that has no right whatsoever in relation to God’s promises (as the heathen have none). The next relative cannot redeem Ruth (chap. 3:12 the relative being a picture of the law of Sinaï). But Boaz the ancestor and type of Jesus Christ takes pity on her.