Part 55 of the David Pawson 'Unlocking the Bible' Podcast series 
David Pawson says that Zephaniah was a descendant of the last good king, but now, after evil kings, there was a boy king on the throne, Josiah. What kind of king would he become? The whole nation was in chaos, having had bad examples on the throne, and God sent Zephaniah as his prophet. His job was to try to pull the nation  of Judah back to God before He would have to exile them as He had the northern 10 tribes already. Zephaniah warns the people of Judah and also the lands around them that there is coming a Day of the Lord when accounts must be settled, but there is time to repent and deflect punishment. Interestingly, God had brought the Philistines to Canaan at the same time as he had brought his chosen people - as an instrument of discipline for his people. David says it’s much better to have the discipline of our Father God now than to reap eternal punishment. Zephaniah is letting the people know that the choice between God’s justice and his mercy is theirs. God’s last word was always to choose his mercy. For all Zephaniah’s and good King Josiah’s efforts, the people wouldn’t listen.