Kommentar zu Schemot 16:36

עשירית האפה [THE OMER] IS THE TENTH PART OF AN EPHAH — The Ephah is three Seahs, and the Seah is six Kabs, and the Kab is four Logs and the Log has the capacity of six eggs: it follows, therefore, that the tenth of an Ephah has the capacity of forty-three and a fifth eggs — and this is the minimum quantity of dough for the Challa (the minimum quantity to which applies the injunction to separate a portion of the dough; cf. Numbers 15:20), and the measure for the meal offering (cf. Rashi on Eruvin 83b).

והעומר עשירית האיפה הוא, “the omer was equivalent to one tenth of the measure known as eyphah.” Rashi in Kidushin 15 explains that 1 איפה =3 סאין, which in turn =6 קבין, which are equivalent to 4 לוגין, each לוג equaling 6 eggs; this means that the daily ration of manna per Israelite was equivalent to a quantity equaling 43,2 eggs. Based on this fact the sages determined that a dough of that amount is subject to the provisions of challah; this is also the maximum amount of dough to be prepared in one lot for baking matzot for Passover.
The reason that the Torah waited until the end of the whole paragraph to tell us the amount of manna G’d assigned to each person daily instead of telling us this when we were told that each person found he had collected 1 omer per head (household member) in verse 16, is because the Torah did not want to interrupt the train of thought we are to entertain when reading about the manna and what is connected with it. If you will examine the paragraph you will find that there were actually three logical points at which this information would have been pertinent. If the Torah deliberately refrained from using any of these opportunities it clearly had a reason for this.
It is also possible that the Torah reserved mentioning this information in order to link it to what follows, i.e. the events at Refidim. It is a well known psychological fact that when a person enjoys material blessings in abundance he becomes less meticulous in serving the Lord and he develops a certain laxity in his approach to Mitzvah-performance, just as he can afford to be lax in his concern for his daily bread. He will not be likely to develop this laxity if he is only just able to feed himself and his family as he is constantly aware of the need of G’d’s goodwill on a daily basis and will make an effort to remain in G’d’s good graces. The Torah tells us that the Israelites became delinquent in their Mitzvah-performance although their daily ration was not so abundant that they could have been expected to develop laxity. As a result of this unwarranted laxity, Amalek (17,8) attacked them. The name רפידים is equated by our sages with רפה, weak, i.e. their Torah-observance weakened. This is the conceptual linkage between this new paragraph and the story about the manna preceding it.
The Torah could have described the amount of manna the Israelites received daily in terms other than “1 tenth of an eiphah.” Why did it choose to mention that it was “1 tenth“ of something? Perhaps the reason for mentioning “1 tenth” is the same as the fact that מעשר, “the tithe” which the farmer has to give to the Levite is “1 tenth.” The Israelites, while in the desert were considered as “sacred bodies,” something akin to angels with bodies. When they would consume this delicate heavenly food their thoughts may have concentrated on the “tenth” emanation and all the holy concepts involved in such contemplations. Perhaps the best example is Exodus 24,11: “they beheld (a vision) of G’d and they ate and they drank.” Perhaps their very eating of such celestial food as the manna is what enabled those אצילי בני ישראל, the most noble group of Israelites, to become privy to such visions at such a time. When we couple this with the proximity to the הר האלו-הים, the mountain of G’d, Sinai, around which all this took place it is not really so remarkable at all. They joined the select elite of which Isaiah said יילכו ולא ייעפו, “they keep walking without becoming fatigued.”

Consequently 1/10. . . [Rashi knows this] because an eiphoh is 432 eggs in total. A tenth of 400 is 40, and a tenth of 30 is 3. 2 eggs remain. If you divide each remaining eggs into 5 parts, then 2 eggs make 10 parts. A tenth of this is 1/5 of an egg. (Maharshal)

V. 36. עשירית האיפה ward später das normale Grundmaß aller מנחות, somit Ausdruck des die Nahrung einer Menschenpersönlichkeit repräsentierenden Quantums vor Gott. Dieses Maß selbst überträgt somit schon die Mannagesinnung auf die vor Gott zu gedenkende Menschennahrung. Ist ja vielleicht selbst מנחה, wenn das מ zur Wurzel gehört, also מנה selbst mit מנה, der Wurzel von מן, und sodann in der Bedeutung als מָנָה, verwandt.

והעומר, “and the amount known as omer, etc;

עשירת האיפה הוא, is equivalent to the well known measure eypha, a measure used for measuring grain.