Then, i.e. when they were upon their march from Rephidim to Horeb, Deu_25:17,18.
The ground of the quarrel was the prosecution of the old hatred of Esau a against Jacob, and-the revenging of themselves and their father upon the posterity of Jacob; for which they thought this the fittest season, they being now great and potent people, Num_24:20, and Israel now weak, and unarmed, and dispirited with long servitude.