Charles H. Spurgeon on Psalms 37:30

The mouth of the righteous speaketh wisdom. Where the whole Psalm is dedicated to a description of the different fates of the just and the wicked, it was meet to give a test by which they could be known. A man's tongue is no ill index of his character. The mouth betrays the heart. Good men, as a rule, speak that which is to edifying, sound speech, religious conversation, consistent with the divine illumination which they have received. Righteousness is wisdom in action, hence all good men are practically wise men, and well may the speech be wise. His tongue talketh of judgment. He advocates justice, gives an honest verdict on things and men, and he foretells that God's judgments will come upon the wicked, as in the former days. His talk is neither foolish nor ribald, neither vapid nor profane. Our conversation is of far more consequence than some men imagine.