The Omer — permits the nation
הָעֹמֶר הָיָה מַתִּיר בַּמְּדִינָה
New grain permitted everywhere in EY — and the world. The global prohibition of Chadash (mishnah 1) is lifted the moment the Omer is sacrificed. Before the Omer: Menachos, Bikkurim, and Minchas Behema (Nesachim) cannot be brought. If brought, pasul — absolutely invalid.
הַמִּשְׁנָה
שֶׁבֵּין
שְׁנֵי הָעוֹלָמוֹת
◆
The Omer's world ends here. The Shtei HaLechem's world begins.
The Shtei HaLechem — permits the Temple
שְׁתֵּי הַלֶּחֶם בַּמִּקְדָּשׁ
New-grain minhaos permitted in the Temple. Before: they cannot be brought. Should not bring — but if brought, kasher — valid after the fact. The Shtei HaLechem's permission is less absolute.
Before the Omer — pasul / absolutely invalid
וְאִם הֵבִיא — פָּסוּל
Before the Omer, the new grain has not been permitted even for ordinary eating. A minhah brought from it is not consecrated at all — there is no sanctity to the offering, only violation. It must be disqualified entirely.
Before the Shtei HaLechem — kasher b'dieved / valid after the fact
וְאִם הֵבִיא — כָּשֵׁר
After the Omer, new grain has been permitted to ordinary people. The restriction on Temple minhaos before the Shtei HaLechem is l'chatchilah only — an ideal ordering. If brought, the grain is already permitted for commoners, so the offering is valid. The Shtei HaLechem's permission is not as fundamental as the Omer's.
Question worth exploring: does this kasher b'dieved apply equally to a korban tzibbur, or only to a korban yachid? The logic of the mishnah — that the grain is already permitted to commoners — would seem to apply to individual offerings. Whether communal offerings are held to a stricter standard and would remain pasul until the Shtei HaLechem is brought may be addressed in the Gemara (Menachos 5b) and later poskim.
The Yavneh beis midrash story — Mishnat Eretz Yisrael on Menachos 10:6
R' Tarfon argued at Yavneh: just as minhaos are pasul before the Omer, so they should be pasul before the Shtei HaLechem. A student, Yehudah ben Nachman, refuted him brilliantly: after the Omer, wheat is already permitted to commoners — the Shtei HaLechem does not unlock the grain, it merely unlocks the Temple. So the analogy fails. R' Akiva saw the argument and his face glowed — then he rebuked Yehudah for showing off in front of R' Tarfon. R' Yehuda the narrator adds: "It was Pesach when this happened. When I came for Shavuos and asked where Yehudah ben Nachman was, they told me — he has gone." The most vivid beis midrash story in the series.