“…You must bring an omer, the beginning of your harvest, to the kohen… You shall not eat bread or parched grain or fresh grain, until this day…” – Vayikra 23:10-14

וַהֲבֵאתֶם אֶת עֹמֶר רֵאשִׁית קְצִירְכֶם אֶל הַכֹּהֵן . . וְלֶחֶם וְקָלִי וְכַרְמֶל לֹא תֹאכְלוּ עַד עֶצֶם הַיּוֹם הַזֶּה – ויקרא כג, י-יד

The Omer is an offering of barley flour that is brought in the Beis Hamikdash on the second day of Pesach. Until the harvesting and offering of the Omer, the Torah prohibits us from partaking of the new year’s crops.

Most other flour offerings in the Temple were from wheat flour. In comparison to wheat, barley is regarded as animal food (see Mishna, Sotah 2:1). Thus, in terms of the spiritual application of this mitzvah, the Omer offering from barley flour represents the early stages in a person’s spiritual development, when his “animal” within is still untamed. He must therefore focus on “sacrificing” his animal, constraining and subduing his selfish or negative impulses.

Accordingly, we can also explain why we may not partake of the new produce until we offer the Omer. For before deriving personal benefit from any grain of this year’s crop, we must ensure that our “barley,” our animalistic tendencies, are under control. By doing so at the start of the harvest, we make certain that even our mundane use of this year’s grain will be “for the sake of Heaven,” to further and facilitate our service of G-d.

—Likutei Sichos, vol. 32, pp. 136-137