kid'-niz (always in the plural: kelayoth; nephroi; Latin renes, whence the English "reins"): "Reins" and "kidneys" are synonyms, but the King James Version undertook a distinction by using the former word in the figurative, the latter in the literal passages. the English Revised Version has followed the King James Version exactly, but the American Standard Revised Version has retained "reins" only in Job 16:13; La 3:13; Re 2:23, elsewhere substituting "heart," except in Ps 139:13, where "inward parts" is used. the King James Version and the English Revised Version also have "reins" for chalatsayim, in Isa 11:5 (the American Standard Revised Version "loins"). The physiological function of the kidneys is not referred to in the Bible, but has been introduced (quite wrongly) by the King James Version margin to Le 15:2; 22:4.
⇒See a list of verses on KIDNEY in the Bible.
(1) The kidneys owe their importance in the Bible partly to the fact that they are imbedded in fat, and fat of such purity that fat of the kidneys was a proverbial term for surpassing excellence (De 32:14 margin). For the visceral fat was the part of the animal best adapted for sacrificial burning, and hence, came to be deemed peculiarly sacred (Le 7:22-25; 1Sa 2:16). Accordingly, the kidneys with the fat surrounding them were burned in every sacrifice in which the entire animal was not consumed, whether in peace (Le 3:4,10,15; 9:19), sin (Ex 29:13; Le 4:9; 8:16; 9:10), or trespass, (Le 7:4) offerings; compare the "ram of consecration" (Ex 29:22; Le 8:25). So in Isa 34:6, "fat of the kidneys of rams" is chosen as a typical sacrificial term to parallel "blood of lambs and goats." (2) The position of the kidneys in the body makes them particularly inaccessible, and in cutting up an animal they are the last organs to be reached. Consequently, they were a natural symbol for the most hidden part of a man (Ps 139:13), and in Job 16:13 to "cleave the reins asunder" is to effect the total destruction of the individual (compare Job 19:27; La 3:13). This hidden location, coupled with the sacred sacrificial use, caused the kidneys to be thought of as the seat of the innermost moral (and emotional) impulses. So the reins instruct (Ps 16:7) or are "pricked" (Ps 73:21), and God can be said to be far from the reins of sinners (Jer 12:2). In all of these passages "conscience" gives the exact meaning. So the reins rejoice (Pr 23:16), cause torment (2 Esdras 5:34), or tremble in wrath (1 Macc 2:24). And to "know" or "try the reins" (usually joined with "the heart") is an essential power of God's, denoting His complete knowledge of the nature of every human being (Ps 7:9; 26:2; Jer 11:20; 17:10; 20:12; The Wisdom of Solomon 1:6; Re 2:23). See FAT; PSYCHOLOGY; SACRIFICE. Compare RS 2, 379-80, and for Greek sacrificial parallels Journal of Philology,XIX (1890), 46. The anatomical relations are well exhibited in the plate in Sacred Books of the Old Testament, "Leviticus."
Burton Scott Easton