Calvin's Commentaries, Vol. 29: Habakkuk, Zephaniah, and Haggai, tr. by John King, [1847-50], at sacred-texts.com
Calvin’s Preface to zephaniah.
Zephaniah is placed the last of the Minor Prophets who performed their office before the Babylonian Captivity; and the inscription shows that he exercised his office of teaching at the same time with Jeremiah, about thirty years before the city was destroyed, the Temple pulled down, and the people led into exile. Jeremiah, it is true, followed his vocation even after the death of Josiah, while Zephaniah prophesied only during his reign.
The substance of his Book is this: He first denounces utter destruction on a people who were so perverse, that there was no hope of their repentance; — he then moderates his threatening, by denouncing God’s judgments on their enemies, the Assyrians, as well as others, who had treated with cruelty the Church of God; for it was no small consolation, when the Jews heard that they were so regarded by God, that he would undertake their cause and avenge their wrongs. He afterwards repeats again his reproofs, and shortly mentions the sins which then prevailed among the elect people of God; and, at the same time, he turns his discourse to the faithful, and exhorts them to patience, setting before them the hope of favor, provided they ever looked to the Lord; and provided they relied on the gratuitous covenant which he made with Abraham, and doubted not but that he would be a Father to them, and also looked, with a tranquil mind, for that redemption which had been promised to them. This is the sum of the whole Book.