If no sensible spring sends forth sweet and bitter water from one opening, and if neither fig tree bears olives nor vine figs, then this is clear.
One heart of man, this noetic spring of speech, and the same mouth, which is the opening of the heart, cannot naturally utter opposite words: blessing and cursing, praise and condemnation.
Such things are uttered only when the heart is changed by choice toward evil. After being meek and peaceful, blessing and praising the brethren, it becomes wild and rebellious through anger contrary to nature.
Then it already gives birth to, and pours forth, curses and condemnations against the brethren.
God of all spoke of such men through the prophet Hosea: "Their hearts are divided; now they shall perish" (Hos 10:2).
Such things ought not to be in you Christians, he says. Otherwise you will prove worse than soulless and insensible creatures.
For they preserve the natural laws of nature and accept nothing contrary to nature. But you, rational men, through your inattention, bring forth fruits contrary to nature.
By free choice you change the sweetest spring of the heart into the bitterest, growing angry and making reproaches and insults against your brothers.
By this you show yourselves to be something else. More than this, by this action you become divided and no longer reveal what you ought to be by nature.
Therefore the great Paul compared such men to tombs and to the poison of asps, saying: "Their throat is an open tomb; with their tongues they have deceived.
"The poison of asps is under their lips; their mouth is full of cursing and bitterness. Their feet are swift to shed blood; destruction and misery are in their ways, and the way of peace they have not known.
"There is no fear of God before their eyes" (Rom 3:13-18).