Fasting is the soul of prayer, mercy is the lifeblood of fasting. Let no one try to separate them; they cannot be separated. If you have only one of them or not all together, you have nothing. So if you pray, fast; if you fast, show mercy; if you want your petition to be heard, hear the petition of others. If you do not close your ear to others you open God’s ear to yourself.
When you fast, see the fasting of others. If you want God to know that you are hungry, know that another is hungry. If you hope for mercy, show mercy. If you look for kindness, show kindness. If you want to receive, give. If you ask for yourself what you deny to others, your asking is a mockery.
Let this be the pattern for all men when they practice mercy: show mercy to others in the same way, with the same generosity, with the same promptness, as you want others to show mercy to you.
Therefore, let prayer, mercy and fasting be one single plea to God on our behalf, one speech in our defense, a threefold united prayer in our favor...
Fasting bears no fruit unless it is watered by mercy. Fasting dries up when mercy dries up. Mercy is to fasting as rain is to the earth. However much you may cultivate your heart, clear the soil of your nature, root out vices, sow virtues, if you do not release the springs of mercy, your fasting will bear no fruit.
When you fast, if your mercy is thin your harvest will be thin; when you fast, what you pour out in mercy overflows into your barn. Therefore, do not lose by saving, but gather in by scattering. Give to the poor, and you give to yourself. You will not be allowed to keep what you have refused to give to others.
--St. Peter Chrysologus