Explanatory Notes on the Whole Bible, by John Wesley, [1754-65], at sacred-texts.com
psa 120:4Arrows - 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.
psa 120:5Mesech - 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.