John 5:4

an angel, &c.--This miracle differed in two points from all other miracles recorded in Scripture: (1) It was not one, but a succession of miracles periodically wrought: (2) As it was only wrought "when the waters were troubled," so only upon one patient at a time, and that the patient "who first stepped in after the troubling of the waters." But this only the more undeniably fixed its miraculous character. We have heard of many waters having a medicinal virtue; but what water was ever known to cure instantaneously a single disease? And who ever heard of any water curing all, even the most diverse diseases--"blind, halt, withered"--alike? Above all, who ever heard of such a thing being done "only at a certain season," and most singularly of all, doing it only to the first person who stepped in after the moving of the waters? Any of these peculiarities--much more all taken together--must have proclaimed the supernatural character of the cures wrought. (If the text here be genuine, there can be no doubt of the miracle, as there were multitudes living when this Gospel was published who, from their own knowledge of Jerusalem, could have exposed the falsehood of the Evangelist, if no such cure had been known there.

— Jamieson-Fausset-Brown Commentary (public domain)