If someone is judged worthy to receive the gift of knowledge but allows his heart to be full of bitterness or rancor or aversion to another, it is as if he had been struck in the eye by a thornbush. That is why knowledge is no good without charity.
You can see that a city is prosperous by the wealth of goods for sale in the market. Land too we call prosperous if it bears rich fruit. And so also the soul may be counted prosperous if it is full of good works of every kind. But first of all it has to be farmed energetically. Then it must be watered by abundant streams of heavenly grace for it to bring forth fruit, some thirty fold, some sixty fold, and some a hundred fold. The soul only acquires goodness and the capacity of fulfilling its duties if it has the grace of God On the other hand, what is uglier or more disgusting than a soul given over to base passions? Look at the hot-headed person: he is like a wild beast. Consider the slave of lust or gluttony: who can bear the sight of him? Pity the victim of melancholy whose spirit is totally prostrated. It is for us to seek to acquire beauty so that the Bridegroom, the Lord, may welcome us into his presence and say, “You are utterly fair, my love, and there is no flaw in you.” (Song of Sol 4:7)
When despondency seizes us, let us not give in to it. Rather, fortified and protected by the light of faith, let us with great courage say to the spirit of evil: 'What are you to us, you who are cut off from God, a fugitive for Heaven, and a slave of evil? You dare not do anything to us: Christ, the Son of God, has dominion over us and over all. Leave us, you thing of bane. We are made steadfast by the uprightness of His Cross. Serpent, we trample on your head.'
If you have received from God the gift of knowledge, however limited, beware of neglecting charity and temperance. They are virtues which radically purify the soul from passions and so open the way of knowledge continually.