“I will bless the LORD, who hath given me counsel: my reins also instruct me in the night seasons.” Psalm 16:7
The meaning of reins in the Bible goes beyond the physical bodypart. In Psalm 7:9 God tries the reins, in Psalm 26:2 as well, and in Psalm 16 we are instructed by our reins. Our heart too is tried and tested. Tested is what is in our heart and mind: are these lies and delusions from man (‘wisdom’ of the world)? Or is it His truth (which is foolishness to the world)? In Psalm 16 David’s reins instruct him from the counsel that YHWH has given him (verse 7): from His truth that David stored in his ‘reins’. David writes that he has set YHWH always before him, like Paul he looks at the things he does not see, which are eternal. And that is what makes David’s heart glad (verse 9).
“While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal; but the things which are not seen are eternal.” 2 Corinthians 4:18
And that is the path of life (verse 11).
During the sacrificial rituals, the kidneys are always specifically mentioned. The kidneys had to be burned on the altar (Exodus 29:13). This shows that God wants us to offer our ‘reins’ to Him. He desires that we sacrifice all that is in our reins that is not of Him.
“For thou desirest not sacrifice; else would I give it: thou delightest not in burnt offering. The sacrifices of God are a broken spirit: a broken and a contrite heart, O God, thou wilt not despise.” Psalm 51:16, 17
“For I desired mercy, and not sacrifice; and the knowledge of God more than burnt offerings.” Hosea 6:6
YHWH desires that we know Him, and knowing Him starts with filling our heart and mind with His truth.
David’s reins instructed him His truth. What are your reins instructing you? What will God find when He searches your reins?
“and all the churches shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works.” Revelation 2:23