A big theme in the book of Ruth is the providence of God. I like how John Piper describes providence as God’s purposeful sovereignty. God is in control of all things (He is SOVEREIGN) and the exercise of His sovereignty in our lives and in the world is what we would describe as providence.
Daniel Block speaks about the theme of God’s providence in Ruth in His commentary:
“the book [of Ruth] is more about the providence of God than the deeds of human beings” (607)
Ruth “must be interpreted as a glorious account of divine providence. Underlying every episode is God’s determination to produce David the king from the depressing and chaotic Israelite environment during the days of the judges.” (610)
“the events are carefully controlled by the divine hand so that Ruth happens to stumble upon Boaz, Boaz responds positively to Ruth’s brash proposition, and the first candidate concedes to Boaz the rights of the redeemer” (615)
