That mouth was created by God to glorify and praise Him, to confess the Orthodox faith, and to give profitable instruction to one's neighbor.
Concerning falsehood, whose inventor and father is the devil, since he "is a liar and the father of lies" (Jn 8:44), he wrote the same thing more fully in the Epistle to the Ephesians.
He said, "Therefore put away falsehood. Let each of you speak truth with his neighbor, for we are members of one another" (Eph 4:25).
Notice here how the Apostle first spoke of fleshly sins and said, "in which you also once walked."
That is, you Colossians also formerly committed such sins, when as idolaters you were given over to them and served them as slaves.
Then he protects them by commanding that, now that they have been joined to Christ, they should cast away all sins.
"But now you yourselves also put off all these," even these sins that are thought to be smaller: anger, fury, malice, blasphemy, shameful speech, and falsehood.
Thus, after presenting all sins and all virtues, he commands them to avoid the former and to practice the latter, saying in verses 9 and 10:
"Having put off the old man with his deeds, and having put on the new, who is renewed in knowledge according to the image of Him who created him."