An omer is a tenth of an ephah. (Ex. 16:36)

Why is the quantity of an omer described only at the end of the whole chapter? And why is this information important to us nowadays?

Each Jew has within him some minute replica of the 10 heavenly spheres….

Since there is a mystical element in the heavenly food manna, the meaning of 'tenth' is a reference to those mystical properties. Similar considerations underlie the 10 words in Psalms (104:14), describing the process resulting in the production of bread. Also the 10 words in the benediction recited over bread are based on the 10 stages of the process. For this reason, we place our 10 fingers on the bread when reciting the benediction.

Based on Job (38:4), "where have you been", Rabbi Shimon bar Yochai concludes that original Adam incorporated all future mankind within his person. Anyone born subsequently would thus be, in a sense, a part of Adam. Since the soul of the Jew is part of G‑d, each Jew has within him some minute replica of the 10 heavenly spheres which Kabbalists view as the celestial power structure.

[Translation and commentary by Eliyahu Munk]