The Greek word “νεφρός” ( pronunciation: nephrós ) is an ancient Greek word with an unknown etymology and it means “kidney” in the English language [1].

Although, the kidney function and anatomy is known to us nowadays, in the Scripture the word “kidney” is used with a different meaning. It refers to the individual’s true character as it was considered to be the place of emotions, desires and wisdom. [2]

This biblical understanding of kidneys as the centre of conscience, explains why in the following verses, the word “mind” is used instead of “kidneys” in order to translate the Greek word “νεφρούς.” [3]

In the book of Jeremiah 17:10 we read “I, the Lord, search the heart, I test the mind” (NKJV) “ἐγὼ Κύριος ἐτάζων καρδίας καὶ δοκιμάζων νεφροὺς” [4]. Also, in the book of Revelation 2:23 we read “I am He who searches the minds and the hearts” (NKJB) “ἐγώ εἰμι ὁ ἐρευνῶν νεφροὺς καὶ καρδίας” [5].

[1] https://el.m.wiktionary.org/wiki/%CE%BD%CE%B5%CF%86%CF%81%CF%8C%CF%82#%CE%91%CF%81%CF%87%CE%B1%CE%AF%CE%B1_%CE%B5%CE%BB%CE%BB%CE%B7%CE%BD%CE%B9%CE%BA%CE%AC_(grc)

[2] https://jewishlink.news/the-kidneys-in-tanach/

[3] https://biblehub.com/topical/k/kidneys.htm

[4] https://apostoliki-diakonia.gr/bible/bible.asp?contents=old_testament/contents_Ieremias.asp&main=ieremias&file=44.17.htm

[5] https://apostoliki-diakonia.gr/bible/bible.asp?contents=new_testament/contents_apokalipsis.asp&main=apokalipsis&file=4.2.htm