Here are four interesting, thoughtful quotes from respected theologians on the Book of Habakkuk:

Habakkuk 2:4
Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith.

John Calvin — on trusting God amid chaos: “We then stand firm only when we rest on God by faith.” Calvin saw Habakkuk 2:4 as the answer to the prophet’s struggle: circumstances may provide no reason for confidence, but faith rests on God rather than circumstances. (The Gospel Coalition)

Warren W. Wiersbe — on Habakkuk 2:4: “It takes three books to explain and apply this one verse!” Wiersbe was referring to the New Testament use of “the just shall live by his faith” in Romans, Galatians, and Hebrews. (StudyLight)

Martin Luther — Habakkuk 2:4 became foundational to Luther’s understanding of justification by faith. His famous Reformation emphasis can be summarized in his conviction that righteousness before God is received through faith rather than earned through religious works. Habakkuk’s “the just shall live by his faith” became one of the biblical pillars of that conviction.

Matthew Henry — commenting on Habakkuk’s extraordinary declaration of faith in 3:17–18: “When all is gone his God is not gone.” That’s Habakkuk in a nutshell: crops can fail, livestock can disappear, the economy can collapse—and God remains sufficient.