Matthew Henry and continuators on Proverbs 12:17

17 He that speaketh truth sheweth forth righteousness: but a false witness deceit.

Here is, 1. A faithful witness commended for an honest man. He that makes conscience of speaking truth, and representing every thing fairly, to the best of his knowledge, whether in judgment or in common conversation, whether he be upon his oath or no, he shows forth righteousness; he makes it to appear that he is governed and actuated by the principles and laws of righteousness, and he promotes justice by doing honour to it and serving the administration of it. 2. A false witness condemned for a cheat; he shows forth deceit, not only how little conscience he makes of deceiving those he deals with, but how much pleasure he takes in it, and that he is possessed by a lying spirit, Jer. ix. 3-5. We are all concerned to possess ourselves with a dread and detestation of the sin of lying (Ps. cxix. 163) and with a reigning principle of honesty.