Charles H. Spurgeon on Psalms 34:13

Keep thy tongue from evil. Guard with careful diligence that dangerous member, the tongue, lest it utter evil, for that evil will recoil upon thee, and mar the enjoyment of thy life. Men cannot spit forth poison without feeling some of the venom burning their own flesh. And thy lips from speaking guile. Deceit must be very earnestly avoided by the man who desires happiness. A crafty schemer lives like a spy in the enemy's camp, in constant fear of exposure and execution. Clean and honest conversation, by keeping the conscience at ease, promotes happiness, but lying and wicked talk stuffs our pillow with thorns, and makes life a constant whirl of fear and shame. David had tried the tortuous policy, but he here denounces it, and begs others as they would live long and well to avoid with care the doubtful devices of guile.