The focus of this book is the problem of God’s judgment on Israel. Habakkuk is trying to wrestle through the fact that God is judging the nation, while other nations (seemingly more sinful) are going unpunished. How can this be the work of a loving God? Since he mentions the Chaldeans, this book is probably dated after the fall of Jerusalem in 605 BC. Archer dates it a little bit before this time.
The prophet wonders why God is allowing evil in Israel. God tells him that he is going to bring Babylon as an agent of his judgment (vv.5-6). But why would God use these evil people to judge his people, who are less evil (v.13)?
Habakkuk decides to stay as a watchman (v.1). God is judging the nation of Israel because of their wickedness. But he promises that the righteous shall live by faith (v.4). This is a passage often repeated in the NT. It shows that faith is the key to being delivered from the judgment of God.
He prays for mercy (v.2). He learns that he needs to wait on God’s judgment for the nations (v.16).