“Two men went up into the temple to pray, one a Pharisee and the other a tax collector. The Pharisee stood and prayed thus with himself, ‘God, I thank thee that I am not like other men, extortioners, unjust, adulterers, or even like this tax collector. I fast twice a week, I give tithes of all that I get.’ But the tax collector, standing far off, would not even lift up his eyes to heaven, but beat his breast, saying, ‘God, be merciful to me a sinner!’ I tell you, this man went down to his house justified rather than the other; for every one who exalts himself will be humbled, but he who humbles himself will be exalted.” (Luke 18:10-14)
St John Chrysostom comments:
“I speak not of such a fast as most persons keep, but of real fasting; not merely abstinence from meats, but from sins as well. For the nature of a fast is such that it does not suffice to deliver those who practice it unless it is done according to a suitable law. So that when we have gone through the labor of fasting we do not lose the crown of fasting, we must understand how and in what manner it is necessary to conduct the business since the Pharisee also fasted, but afterward went away empty and destitute of the fruit of fasting. The Publican did not fast, and yet he was accepted in preference to him who had fasted in order that you may learn that fasting is unprofitably unless all other duties accompany it.
Fasting is a medicine. But like all medicines, though it be very profitable to the person who knows how to use it, it frequently becomes useless (and even harmful) in the hands of him who is unskilled in its use.
I have said these things not that we may disparage fasting, but that we may honor fasting. For the honor of fasting consists not in abstinence from food, but in withdrawing from sinful practices, since he who limits his fasting only to abstinence from meats is one who especially disparages fasting.” (DAILY READINGS FROM THE WRITINGS OF ST JOHN CHRYSOSTOM, pp 3-4)