Charles H. Spurgeon on Psalms 50:19

Thou givest thy mouth to evil. Sins against the ninth commandment are here mentioned. The man who surrenders himself to the habit of slander is a vile hypocrite if he associates himself with the people of God. A man's health is readily judged by his tongue. A foul mouth, a foul heart. Some slander almost as often as they breathe, and yet are great upholders of the church, and great sticklers for holiness. To what depths will not they go in evil, who delight in spreading it with their tongues? And thy tongue frameth deceit. This is a more deliberate sort of slander, where the man dexterously elaborates false witness, and concocts methods of defamation. There is an ingenuity of calumny in some men, and, alas! even in some who are thought to be followers of the Lord Jesus. They manufacture falsehoods, weave them in their loom, hammer them on their anvil, and then retail their wares in every company. Are these accepted with God? Though they bring their wealth to the altar, and speak eloquently of truth and of salvation, have they any favour with God? We should blaspheme the holy God if we were to think so. They are corrupt in his sight, a stench in his nostrils. He will cast all liars into hell. Let them preach, and pray, and sacrifice as they will; till they become truthful, the God of truth loathes them utterly.