Midrash su Esodo 16:33

And Moses said unto Aaron: “Take a jar and put an omerful of manna therein” (Exod. 16:33). I would not know of what substance the jar was fashioned, whether of silver or of gold or of iron or of lead, except for the fact that Scripture says tzintzenet, a word that suggests something that keeps a thing cooler than anything else.¹⁴Jastrow tells us that tzintzenet is in the text because it glistened more than any other thing (i.e., it was a glazed earthen vessel). And that could only be a clay vessel. And put an omerful of manna therein. R. Eleazar held: It was stored there for future generations. While R. Eliezer was of the opinion that it was put there for the Messianic era, for the time about which the prophet Jeremiah said to Israel: Why do you not devote yourself to the Torah? And they replied: If we do, how shall we obtain our sustenance? Then they brought forth the jar of manna and said: O generation; see the word of the Lord: Have I been a wilderness unto Israel? or a land of thick darkness? Wherefore say My people: “We roam at large; we will come no more unto Thee?” (Jer. 2:31). Your fathers occupied themselves with the Law, and see how they were fed; concern yourselves with the Law, and I shall feed you from this jar. This is one of the three things that Elijah will restore to Israel in the future: the jar of manna, the bottle of anointing oil, and the bottle of sprinkling water. Others add, Aaron’s rod with its ripe almonds and blossoms, as is said: Put back the rod of Aaron before the testimony, to be kept there, for a token against rebellious children (Num. 17:25).