Barley is a lowly grain in the Jewish tradition. It is associated more with animal food than human fare. As such it relates to those drives and behaviours that we share with the animal kingdom.
The Zohar associates barley with the left column of the Tree of Life. The left side is the pillar of constriction and serves as the boundary-setting force in the universe. The Hebrew term for barley (Se'orah) engenders this association; it derives from the word for hair (Se'ar) and relates as well, to the word for “measured portion” (Shi'ur). In Kabbala, hair symbolizes a channel that only allows a metered amount of light to pass at any given moment — only as much as can fit inside its narrow conduit.
Barley's spiritual roots thus connect it to the sefira of Discernment (Binah), which sits atop the left pillar. Binah 's discriminating intelligence rightly belongs to the left side. It breaks down a subject into discrete units and organizes them into categories with definitional boundaries that distinguish each group from the next. According to Kabbala, boundary-setting is a left-sided process .
This is why the heart, as the seat of desire, is situated on the left side of the body, for its longings are the inevitable consequence of boundaries:
These mutual longings drive creation forward. They are the dynamo that keeps things moving and evolving. At their root they are only good.