(32) Moses said, “This is what the LORD has commanded: Let one omer of it be kept throughout the ages, in order that they may see the bread that I fed you in the wilderness when I brought you out from the land of Egypt.” (33) And Moses said to Aaron, “Take a jar, put one omer of manna in it, and place it before the LORD, to be kept throughout the ages.” (34) As the LORD had commanded Moses, Aaron placed it before the Pact, to be kept. (35) And the Israelites ate manna forty years, until they came to a settled land; they ate the manna until they came to the border of the land of Canaan. (36) The omer is a tenth of an ephah.
ד"א: כי קרוב הוא – בקרוב ירשו כנעניים את הארץ, שנא' (בראשית טו) "ודור רביעי ישובו הנה". לא הביאן הקב"ה דרך פשוטה לארץ ישראל, אלא דרך המדבר. אמר הקב"ה: אם אני מביא עכשיו את ישראל לארץ – מיד מחזיקים אדם בשדהו ואדם בכרמו, והן בטלים מן התורה! – אלא אקיפם במדבר ארבעים שנה, שיהיו אוכלין מן ושותין מי הבאר, והתורה נכללת בגופן. מכאן היה ר' שמעון אומר: לא ניתנה התורה לדרוש אלא לאוכלי המן, ושוין להם אוכלי תרומה.
The Holy One Blessed be He did not bring them directly to Eretz Yisrael but by way of the desert, saying: If I bring them there now, immediately each man will seize his field, and each man his vineyard and they will neglect Torah study. Rather, I will keep them in the desert forty years, eating manna and drinking from the well, and the Torah will be absorbed in their bodies. From here R. Shimon would say: The Torah was given to be expounded only by the eaters of manna, and, like them, the eaters of terumah (i.e., the Cohanim).