The church, you see, is a pharmacy of the spirit, and those who come here ought acquire some appropriate remedies, apply them to their own complaints, and go off the better for it. I mean, blessed Paul confirms this, that mere listening without showing practical response is of no value, when he says: “It is not after all, the listeners to the law who are at rights with God, but doers of the law who are set at rights.” Christ, too, in his preaching said: “Not everyone saying to me, Lord, Lord, will enter the kingdom of heaven, but the one who does the will of my Father in heaven.” Accordingly, dearly
beloved, since we know that no benefit comes to us from listening unless it is brought to its completion in the good works that follow, let us not be listeners only but doers, so that the works following the words may be for us grounds for confidence…
when doctors intend to prescribe medicine to patients anxious to get rid of putrid, harmful fluids, they direct them to abstain from bodily food lest it be a hindrance to the power of the medicine instead of its having the effect of demonstrating its true properties. So much the more should we, on the point of receiving that spiritual medicine the benefit of fasting-purify our thinking and render our mind alert lest it be sodden with drink and find useless and unprofitable what should be of benefit in the exercise.
St. John Chrysostom, homily on Genesis