The Hebrew noun kilyah (plural kelayot) refers literally to the kidney and figuratively to the deepest seat of human emotion, thought, and conscience. In ancient Israelite understanding, the kidneys were considered the center of the innermost self, alongside the heart — together representing the totality of the inner person.
The paired phrase 'heart and kidneys' (lev we-kelayot) appears in Jeremiah 11:20, 17:10 where God is described as the one who 'tests the heart and the kidneys' — a declaration of divine omniscience penetrating to the most hidden depths of human motivation.
Psalm 16:7 uses the kidneys as the organ of divine instruction: 'Even at night my kidneys instruct me' (often translated 'my heart'). This captures an inner moral compass — conscience shaped by God's word that continues to guide even in the unconscious hours.