He desired that they remember and commemorate his sacrifice and death as their Redeemer. The emblems he chose for this memorial service were simple but profoundly significant. In doing so, Jesus acquiesced to his Father's will and plan for the salvation of the world. Leaven is a symbol of sin. Leaven produces fermentation, and when mixed with flour, makes it light.
Fermentation is caused by a microscopic fungus.
As we review the meaning of leaven, we see that as far as our blessed Lord was concerned, the fungus of sin was clearly missing from his perfect life. Bread was very important in biblical times. In early Babylonian history, grain was the basic unit for the system of weights. Wheat was highly prized. After threshing and winnowing, it was crushed or ground.