Jamieson, Fausset and Brown on Exodus 4:29-31

29-31. Moses and Aaron went--towards Egypt, Zipporah and her sons having been sent back. (Compare Ex 18:2).

gathered ... all the elders--Aaron was spokesman, and Moses performed the appointed miracles--through which "the people" (that is, the elders) believed (1Ki 17:24; Jos 3:2) and received the joyful tidings of the errand on which Moses had come with devout thanksgiving. Formerly they had slighted the message and rejected the messenger. Formerly Moses had gone in his own strength; now he goes leaning on God, and strong only through faith in Him who had sent him. Israel also had been taught a useful lesson, and it was good for both that they had been afflicted.