See here, 1. How industrious a good man is, by communicating his goodness, to do good with it: His mouth, the outlet of his mind, is a well of life; it is a constant spring, whence issues good discourse for the edification of others, like streams that water the ground and make it fruitful, and for their consolation, like streams that quench the thirst of the weary traveller. It is like a well of life, that is pure and clean, not only not poisoned, but not muddled, with any corrupt communication. 2. How industrious a bad man is, by concealing his badness, to do hurt with it: The mouth of the wicked covers violence, disguises the designed mischief with professions of friendship, that it may be carried on the more securely and effectually, as Joab kissed and killed, Judas kissed and betrayed; this is his sin, to which the punishment answers (Pro 10:6): Violence covers the mouth of the wicked; what he got by violence shall by violence be taken from him, Job 5:4, Job 5:5.