The heart of fools is in their mouth: but the mouth of the wise is in their heart.
Read Chapter 21
Hilary of Poitiers
For what good reason would the prophet have said "the tongue meditates injustice," if meditation pertains to the living soul through its rational consciousness, whereas the tongue was not created according to a rational nature proper to it but to be at the service of the rational nature? And yet, another prophet also shows the authoritativeness of a similar inspired and perfect saying when he says, "The heart of fools is in their mouth," meaning that they randomly say things that have no foundation, accustomed as they are to not treating any argument with the deliberation of reason and after meditating on it in the heart but only by the imprudent movement of a rash tongue. If a fool"s heart is in his mouth, it is because he does not say what he has thought but thinks afterwards about what he has said. This refers to the tongue of the fool. Of the tongue of the wise, rather, we read, "The tongue of the wise meditates wisdom." And, "My tongue like the pen of a nimble scribe." The tongue of the wise is born of meditation on wisdom, and therefore of itself, like the pen of a scribe, it does nothing disordered or uncertain. It submits itself, rather, to what has been thought and read, which make it flow nimbly according to the judgment of reason. - "Homilies on the Psalms 51.7"