And thou shalt take all the fat that covereth the inwards, and the caul that is above the liver, and the two kidneys, and the fat that is upon them, and burn them upon the altar.(Exodus 29:13) KJV
We can imagine God holding our spiritual reins like the harness of a horse and directing us. However, there’s another way to understand the reins which ties into our developing hypotheses of the operation of the human body.
Renal (plural noun) the kidneys; the region of the kidneys, or the lower part of the back; (especially in Biblical use) the seat of the feelings or affections, formerly identified with the kidneys.– Renal, definition
The Hebrew word sometimes translated as reins is elsewhere translated as kidneys. This is another usage of the word in modern language, and it’s the origin of the word renal. The kidneys process the blood and filter out toxins and pollution. They influence the chemistry of our blood.