en_tn/jer/42/18.md

as my wrath and my fury

Both of these words are used to describe great anger. (See: rc://en/ta/man/translate/figs-doublet)

my wrath and my fury were poured out

Emotions are described as something that can be poured like water. This description expresses that Yahweh will not hold back from punishing the people of Jerusalem. (See: rc://en/ta/man/translate/figs-metaphor)

an object of cursing and a horror, an object for speaking curses, and something dishonorable.

Yahweh is basically saying the same thing twice for emphasis. The phrase "object of cursing" means others would say they want their enemies to be like the people of Jerusalem because the people of Israel are so miserable.(See rc://en/ta/man/translate/figs-parallelism)

I have been a witness

Yahweh has been the one who makes sure the people of Israel are punished if they do not keep their promise to obey Yahweh's command.