The Omer offering is primarily comprised of barley and is brought at the beginning of Pesach, early during the harvest season. After the Omer has been offered, Jews are allowed to eat from harvested grain of the new crop (chadash). Seven weeks later, the shtei ha-Lechem, an offering composed primarily of wheat, is presented in the Beis ha-Mikdash. As the Jews are already allowed to eat harvested grain of the new crop, the shtei ha-Lechem offering allows Jews to use grain from the new crop in the Temple service.
If the Omer represents man’s belief that all food truly emanates from God (Sefer HaChinuch, 95, 302), why is barley, an inferior grain that is commonly consumed by animals, used instead of wheat? The Sefer HaChinuch (Mitzva 307) posits that in general a person’s heart is swayed by the actions he performs, and Hashem, understanding human nature, commands accordingly. For example, a sin offering, which requires a great expenditure with lengthy procedural necessities, is designed to stir the heart of the sinner towards repentance. In a similar vein, to ingrain within us the idea that our relationship with Hashem is more important than the food that we eat, Hashem commands that wheat and not barley be used for the shtei ha-Lechem. To help set up this contrast, this philosophical dichotomy with which we must approach life, He also commands us to use barley, and not the superior wheat grain, for the omer.