It will come about at that time

This marks the time when Jerusalem has been destroyed by the enemies.

I will search Jerusalem with lamps

Yahweh speaks of knowing about all people of Jerusalem as if he had searched for them with lamps.

They feel safe from trouble.

"say in their heart that Yahweh will not do anything, either good or evil.

This means that they think to themselves.

"Yahweh will not do anything at all"