Charles H. Spurgeon on Psalms 73:21

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.