Verse 4 Sharp arrows of the mighty, with coals of juniper. Arrows — The wrath and vengeance of the mighty God, which in scripture is often compared to arrows, and here to coals of juniper, which burn very fiercely and retain their heat for a long time.
Verse 5 Woe is me, that I sojourn in Mesech, that I dwell in the tents of Kedar! Mesech — Mesech and Kedar are two sorts of people often mentioned in scripture, and reckoned amongst the barbarous nations. But their names are here to be understood metaphorically. And so he explains himself in the next verse.