C.H. Spurgeons's The Treasury of David
Verse 21. The holy poet here reviews his inward struggle and awards himself censure for his folly. His pain had been intense; he says,
Thus my heart was grieved. It was a deep seated sorrow, and one which penetrated his inmost being. Alexander reads it, "My heart is soured." His spirit had become embittered; he had judged in a harsh, crabbed, surly manner. He had become atrabilious, full of black bile, melancholy, and choleric; he had poisoned his own life at the fountain head, and made all its streams to be bitter as gall.
And I was pricked in my reins. He was as full of pain as a man afflicted with renal disease; he had pierced himself through with many sorrows; his hard thoughts were like so many calculi in his kidneys; he was utterly wretched and woebegone, and all through his own reflections. O miserable philosophy, which stretches the mind on the rack, and breaks it on the wheel! O blessed faith, which drives away the inquisitors, and sets the captives free!
EXPLANATORY NOTES AND QUAINT SAYINGS
Verse 21. Thus my heart was grieved, etc. Two similitudes are used, by which his grief and indignation or zeal are described. First, he says his heart boiled over like yeast. The passion which was stirred up in his thoughts he compares to the yeast which inflates the whole mass, and causes it to swell or boil over... The other simile is taken from the internal pains which calculi produce; I was pricked in my reins. They who have felt them are aware of the torture, and there is no need for a long description. It signifies that his great pain was mingled with indignation, and that this came fresh upon him as often as he looked upon the prosperity of the ungodly. Mollerus.
Verse 21. Reins. Before all the other intestines there are the kidneys (twylb, nefroi), placed on both sides of the lumbar vertebrae on the hinder wall of the abdomen, of which the Scripture makes such frequent mention, and in the most psychically significant manner. It brings the most tender and the most inward experience of a manifold kind into association with them. When man is suffering most deeply within, he is pricked in his kidneys ("reins"). When fretting affliction overcomes him, his kidneys are cloven asunder (Job 16:13; compare La 3:13); when he rejoices profoundly, they exult (Proverbs 23:16); when he feels himself very penetratingly warned, they chasten him (Psalms 16:7); when he very earnestly longs, they are consumed away with his body (Job 19:27). As the omniscient and all penetrating knower of the most secret hidden things of man, God is frequently called (from Psalms 7:10 to the Apocalypse) the Trier of the hearts and reins; and of the ungodly it is said, that God is far from their reins (Jeremiah 12:2), that is, that he, being withdrawn back into himself, allows not himself to be perceived by them. Franz Delitzsch.
HINTS FOR PASTORS AND LAYPERSONS