Musar על מיכה 7:5

And it is written (Michah 7:5): "From her who lies in your bosom, guard the doors of your mouth." Scripture has hereby intimated to us that the mouth is like a door. And just as the door of a house has a time to be open and a time to be closed (for if it is always open everything in the house will be lost), so the doors of your mouth have a time to be open — to words of Torah and other essential things, and a time to be closed — to other things.

Thus Zohar relates in Parashas Naso (121b): The falsehood that a person speaks ascends and pierces the firmaments, remaining there until nightfall. Then his soul ascends and takes hold of that statement and tries bringing it before the holy King. This is the meaning of the verse, “Guard the portals of your mouth from the one who lies in your embrace” (Michah 7:5). Later, both the statement and the iniquity he committed thereby are recorded. Therefore fortunate is he who conducts himself without guile.