Zephaniah 1:1
The word of the LORD which came unto Zephaniah the son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hizkiah, in the days of Josiah the son of Amon, king of Judah. The word of the LORD which came unto Zephaniah the son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hizkiah, in the days of Josiah the son of Amon, king of Judah.
The opening line introduces the whole book as the word of the Lord coming to Zephaniah. That coming is placed in the days of Josiah the son of Amon, king of Judah. The prophecies that followed warned plainly that continued apostasy would bring judgment, while also pointing beyond that judgment to a glorious future.
That judgment pronounced against Judah applies also to the judgment of the impenitent world at Christ's second advent, so the book is prophecy for the last day. The destruction and desolation it describes will soon be witnessed universally just as described, as certainly as the desolation of San Francisco was seen. In this it reveals the judgments of God coming upon cities. Therefore everyone must heed the warning and be ready, for the Son of man comes in an hour that is not expected.