Zephaniah says that the word of the Lord is against the Philistines, and that word comes to expression in a first-person declaration of the prophet as he represents the Lord as warrior: I will destroy you until no inhabitant is left.
The end of the Philistines was sure because the hand of the Lord was against them for destruction. This message, however, was for God’s people. He had “previously warned his people that if they did not remain faithful to him, he would destroy ('eibad) them just as he had destroyed ('eibad) the nations who inhabited the land before them (cf. Deuteronomy 8:19–20).”1 And so by this announcement, Judah could know that the day of the Lord would most definitely come in judgment against the rebellious.2
5 Woe to you inhabitants of the seacoast, you nation of the Cherethites! The word of the LORD is against you, O Canaan, land of the Philistines; and I will destroy you until no inhabitant is left.