The second condition is never to fast through vanity but always through humility. If our fast is not performed with humility, it will not be pleasing to God. …
Pagan philosophers fasted thus, and their fast was not accepted by God. Sinners fast in this way, but because they do not have humility it is of no profit at all to them. Now, according to the Apostle, all that is done without charity is not pleasing to God; so I say in the same way, with this great saint, that if you fast without humility your fast is of no value. For if you have not humility, you have not charity, and if you are without charity you are also without humility. It is almost impossible to have charity without being humble and to be humble without having charity. These two virtues have such an affinity with one another that the one can never be without the other.
…To fast through vanity is to fast through self-will, since this self-will is not without vanity, or at least not without a temptation to vanity. And what does it mean to fast through self-will? It is to fast as one wishes and not as others wish; to fast in the manner which pleases us, and not as we are ordered or counseled. You will find some who wish to fast more than is necessary, and others who do not wish to fast as much as is necessary. What causes that except vanity and self-will? All that proceeds from ourselves seems better to us, and is much more pleasant and easy for us than what is enjoined on us by another, even though the latter is more useful and proper for our perfection. This is natural is born from the great love we have for ourselves.
You are not, says Our Lord, to look gloomy and melancholic like the hypocrites do when they fast in order to be praised by men and esteemed as great abstainers…. Our Divine Master did not mean by this that we ought to have no care about the edification of our neighbor. Oh, no, for St. Paul says [Phil. 4:5]: Let your modesty be known to all. Those who fast during the holy season of Lent ought not to conceal it, since the Church orders this fast and wishes that everyone should know that we are observing it. We must not, then deny this to those who expect it of us for their edification, since we are obliged to remove every cause of scandal to our brothers. But when Our Lord said: Fast in secret, He wanted us to understand: do not do it to be seen or esteemed by creatures; do not do your works for the eyes of men. Be careful to edify them well, but not in order that they might esteem you as holy and virtuous. Do not be like the hypocrites. Do not try to appear better than others in practicing more fasting and penances than they.