Zephaniah was a prophet (holy man). The Book of Zephaniah is in the Bible (Old Testament).
Zephaniah explained that God would punish many countries because of their evil deeds (Zephaniah chapters 1-2). God would also punish the evil people in Jerusalem (Zephaniah 3:1-5).
So, the people should pray to God (Zephaniah 2:1-3). They must confess their evil deeds to God. And they must be humble.
When these terrible punishments happen, God will protect the people who trust him (Zephaniah 3:9-13). God will rescue them. He loves them. And he will make them glad (Zephaniah 3:14-20).