The people of Judah knew that under Hezekiah, Sennacherib’s Assyrian army was at the walls of Jerusalem and had been repelled–or outlasted. King Josiah had returned the nation to the ways of YHWH–the God of Jacob and Moses–and while the Babylonian Empire was on the rise, I suspect some of them were attracted to the idea of a day of vengeance would come when YHWH come in judgement.
Zephaniah had this to say about the Day of YHWH:
The great day of the Lord is near—
near and coming quickly.
The cry on the day of the Lord is bitter;
the Mighty Warrior shouts his battle cry.
. . . .
Woe to the city of oppressors,
rebellious and defiled!
She obeys no one,
she accepts no correction.
She does not trust in the Lord,
she does not draw near to her God.
Her officials within her
are roaring lions;
her rulers are evening wolves,
who leave nothing for the morning.
Her prophets are unprincipled;
they are treacherous people.
Her priests profane the sanctuary
and do violence to the law.
The Lord within her is righteous;
he does no wrong.
Morning by morning he dispenses his justice,
and every new day he does not fail,
yet the unrighteous know no shame.