The answer is: Blood

Gen 9:4 - An early prohibition, re-affirmed in Lev 7:26.

After the flood, one of the first commands given to humanity was about the sanctity of blood. While it seems like an odd subject to dwell on at first, there's a deeper significance to this mandate. In Genesis 9:4, the idea is not merely about what one can or cannot eat, but rather a profound acknowledgment of life and its connection to the divine.

To ancient cultures, blood was considered the essence of life—a theme echoed throughout many societal customs, where blood sacrifice would signify respect and gratitude towards the divine. The "no blood" rule calls for a certain reverence for life itself. It's echoed in the later Jewish laws found in Leviticus 7:26, revealing the continuity of this thought throughout Biblical narrative.

Interestingly, the image of blood can link to broader themes of redemption and sacrifice—appearing later in the New Testament as a symbol of new covenant and forgiveness through Christ. This marks a consistent weaving throughout scripture: the relationship between sustenance, life, and spiritual significance.

Contextually, after the tumultuous experience of the flood, these instructions acted almost like guidelines for cultivating a respectful and proper society in their newfound world. Imagine facing a sky fresh and clear after the storm, and the community forming a moral basis for how to live anew—talk about a fresh start! It’s remarkable how one small dietary adjustment can symbolize such a great respect for the life that each being represents in the tapestry of creation.