John Gill Commentary Jeremiah 30:12

"For thus saith Jehovah, Thy hurt is incurable, and thy wound grievous." — Jeremiah 30:12 (ASV)

For thus says the Lord, your bruise [is] incurable By themselves or others, in all human appearance; there was no help for them from men; their case seemed desperate; there was no likelihood of their recovery to their former state and glory, as at this day the case of the Jews appears to be; there seems to be no probability of their conversion and restoration; and whenever it is, it will be as life from the dead, (Romans 11:15); like quickening Ezekiel's dry bones, or raising persons from the dead, which none but the hand of omnipotence can effect.

[and] your wound [is] grievous an expression signifying the same as before: the metaphor is taken from a body wounded and bruised in such a manner, as to be past the skill of the most able surgeon to cure it.