Once again, I defer to the introduction of Habakkuk found in the English Standard Version of the scripture. It offers an incredibly helpful overview of this text.
Habakkuk was probably written about 640–615 b.c., just before the fall of Assyria and the rise of Babylon. God used Assyria to punish Israel (722); now he would use Babylon to punish Judah. This prophecy would be fulfilled several decades after Habakkuk, in 586. The “theme question” of Habakkuk is, how can God use a wicked nation such as Babylon for his divine purpose? God judges all nations, said Habakkuk, and even Babylon would eventually be judged (Babylon fell to Persia in 539). But God’s people are held to a higher standard because they have greater revelation. Though God’s ways are sometimes mysterious, “the righteous shall live by his faith” (2:4) while awaiting salvation. These words are quoted three times in the New Testament (Rom. 1:17; Gal. 3:11; Heb. 10:38).
I have appreciated your thoughts the last couple of days (especially the part about God being Irish, since I am too!), because the fact – as you said – that God uses a pagan nation to punish His people, but then punishes that nation for what they did to His people, shows His incomprehensible sovereignty. Romans 9 sheds some good light on this as I’m sure you know, asking the question, how can God harden people’s hearts and then condemn them for their stubbornness. But who are we to question God, the text asks. To us, His ways might seem unfair, but we don’t even have enough wisdom to run our own lives sometimes, let alone run the affairs of all mankind. Good stuff.