en_tn/isa/48/03.md

General Information:

Yahweh continues speaking to the people of Israel.

they came out from my mouth

"Mouth" refers to someone speaking. AT: "I spoke these things" (See: rc://en/ta/man/translate/figs-synecdoche)

your neck muscles tight as iron, and your forehead like bronze

Yahweh compares the tightness of their neck muscles and the hardness of their foreheads to the hardness of iron and bronze. Here, to have a tight neck or a hard forehead is a metaphor that means the people are stubborn. AT: "it is as if your necks were iron and your heads were bronze" (See: rc://en/ta/man/translate/figs-simile and rc://en/ta/man/translate/figs-metaphor)

I declared these things to you beforehand; before they happened I informed you

This is saying the same thing twice for emphasis. (See: rc://en/ta/man/translate/figs-parallelism)