That led them through the deep - They went through the deep on dry land - the waters having divided and left an unobstructed path.
As an horse in the wilderness - As an horse, or a courser, goes through a desert without stumbling. This is a most beautiful image. The reference is to vast level plains like those in Arabia, where there are no stones, no trees, no gullies, no obstacles, and where a fleet courser bounds over the plain without any danger of stumbling. So the Israelites were led on their way without falling. All obstacles were removed, and they were led along as if over a vast smooth plain. Our word ‘wilderness,’ by no means expresses the idea here. We apply it to uncultivated regions that are covered with trees, and where there would be numerous obstacles to such a race-horse. But the Hebrew word (מדבר midbâr) rather refers to “a desert, a waste” - a place of level sands or plains where there was nothing to obstruct the fleet courser that should prance over them. Such is probably the meaning of this passage, but Harmer (Obs. i. 161ff) may be consulted for another view, which may possibly be the correct one.