Ramban

BEHOLD, I WILL ‘MAMTIR’ (CAUSE TO RAIN) BREAD FROM HEAVEN FOR YOU. Rabbi Abraham ibn Ezra wrote that because the manna came down like rain from heaven, He said mamtir, [which is derived from the root matar (rain)]. But we find: ‘yamteir’ (He will cause to rain) coals, fire and brimstone; And the Eternal ‘himtir’ (caused to rain) upon Sodom and upon Gomorrah brimstone and fire. [Brimstone and fire do not come down like rain, and yet Scripture uses the word matar with reference to them!] Perhaps in these cases they accompanied the rain of which the term “coming down” may properly be used. Onkelos’ opinion is that mamtir just means “cause to bring down,” for he translated: “behold, I will cause to bring down.” [However, it has no connection here with rain, as Ibn Ezra would have it.] It is possible that the word mamtir can be associated with the expression ‘kamatarah’ (as a mark) for the arrow, although they are of different roots. (target) is of the root natar (keep), since a target is kept in sight and watched. Mamtir however is of the root matar (rain). Yet, as Ramban concludes, they have a common association, as is explained in the text. Scripture makes use of both terms when speaking of every form of “falling from above.” Thus it is called matarah (target) because they come down like arrows [on a target], and it says, ‘vayamteir’ (And He caused to rain) upon them flesh as the dust, and winged fowl as the sand of the seas. It may be that [Scripture does not use the term mamtir for every form of “falling from above,” but only] for the fowl of heaven. [Therefore, the term, vayamteir in the above — mentioned verse refers only to the winged fowl] because they came down upon them as the rain.
BREAD. Because they made bread out of the manna — as it is written, and they made cakes of it — [Scripture calls it lechem (bread)], for every form of bread is called lechem, not just those of wheat and barley. It says cause to rain bread [although it did not come down in the form of bread, for the meaning thereof is] that He is causing it to come down for them to make it into bread. Similarly: As for the earth, out of it cometh bread, [meaning: “out of it cometh the wheat from which bread is made”]. So also: To bring forth bread out of the earth, which means that He brings forth the wheat from which people make bread. And some scholars. interpret: Behold, I will cause to rain bread, meaning food. Similarly: ‘lechem’ of the offering; For he offereth the ‘lechem’ of thy G-d;, 21:8. When thou sittest ‘lilchom’ with a ruler — all are expressions of food. The correct interpretation is that lilchom means “to eat bread,” and ‘lechem’ of thy G-d, 21:8. is a euphemism, meaning that it is “the food” for G-d even as bread is for man, for we find it said, Man doth not live by bread only.
THAT I MAY TRY THEM, WHETHER THEY WILL WALK IN MY LAW OR NOT. “I.e., whether they will observe the commandments associated with it, such as [the laws] that they should not leave [a remainder] of it until the morning and that they should not go out on the Sabbath to collect it.” Thus the language of Rashi. But this is not correct. (“that” or “for the sake of”) — ‘that’ I may try them — expresses causation in itself, namely, that the manna as such will be their trial, as will be explained, and not the precepts associated with it, as Rashi explained. Rather, the intent [of the trial mentioned here] is as He said, Who fed thee in the wilderness with manna, which thy fathers knew not; that He might afflict thee, and that He might try thee, to do thee good at thy latter end. [The manna itself] was a trial to them, since they had no food in the wilderness and were without recourse to any sustenance except the manna, which they knew not from before and had never heard of from their fathers. Each day’s quantity came down on its day, and they were eagerly desirous for it. Yet with all this, they hearkened to walk after G-d to a place of no food. And so indeed He said to them again, And thou shalt remember all the way in which the Eternal thy G-d hath led thee these forty years in the wilderness, that He might afflict thee, to try thee, to know what was in thy heart, whether thou wouldest keep His commandments, or no., Verse 2. He could have led them by way of the cities that were round about them. Instead, He led them through the wilderness wherein were serpents, fiery serpents, and scorpions, and each day’s quantity of food would come to them only from heaven in order to try them and to do them good at the end so that they would believe in Him forever. I have already explained the matter of “trial” in the commentary on the verse, And G-d tried Abraham. The Rabbi [Moshe ben Maimon] has written in the Moreh Nebuchim i.e., let every one who desires try and see whether it is useful and sufficient to devote himself to the service of G-d.” [on the verse before us, That I may try them, whether they will walk in My law or not, that it means] that “everyone capable of knowledge should know and determine whether there is usefulness in the service of G-d, and whether there is adequate satisfaction in it or not.” But if so, it would have been proper for Him to say, “that He may try them to know!” Now Scripture mentions here only the matter of manna, which was “the bread” which He caused to rain upon them, [and it does not refer to the flesh which He gave them]. However, from that which Moses told them, This shall be, when the Eternal shall give you in the evening flesh to eat, and in the morning bread to the full, we know that everything was told to him. It is only that when a subject is mentioned twice, Scripture shortens it in the report of the command or the narrative, as I have mentioned to you many times. At times, it omits one — [the command or the narrative] — altogether, such a case being the verse written in this section: This is the thing which the Eternal hath commanded: Let an omerful of it [the manna] be kept throughout your generations, and the command [of G-d to Moses] is not recorded at all. This is also the case in many places. But in the opinion of those scholars who say that lechem here means “all food,” it is possible that by saying, Behold, I will cause to rain ‘lechem,’ the meaning refers to both the manna and to the quail, i.e., that He would fulfill their request for bread and flesh. Moses explained that the flesh would be [available] to eat in the evening, and the bread would be [available] in the morning to the full, as is the customary way.