Numbers 21:4 - Matthew Poole's English Annotations on the Holy Bible

By the way of the Red Sea, i.e. which leadeth to the Red Sea, as they must needs do to compass the land of Edom. Because of the way; by reason of this journey, which was long, and troublesome, and preposterous, (for they were now going towards Egypt,) and unexpected, either because they doubted not but their brethren the Edomites would grant them their reasonable request of passing through their land, which disappointment made it worse; or because the successful entrance and victorious progress which some of them had made in the borders of Canaan, made them think they might have speedily gone in and taken possession of it, and so have saved their tedious travels and further difficulties into which Moses had again brought them.