It took me a long while to figure this out in my life, even though it is so simple.
Fasting, which we are obligated to do on Ash Wednesday and Good Friday, and encouraged to do each Friday of the year, is not about pain or discomfort. We are not trying to inflict distress on ourselves so as to win God’s favor in some way or another.
No. Fasting is an opportunity for us to exercise our wills. To master what controls us.
Again, in case this slipped by you, fasting is an act of the will that strengthens the will to pursue what is true, good and beautiful. We fast from food to strengthen us against the devil.
In St. Peter’s epistle, he describes the devil as a roaring lion that seeks someone to devour. The devil wants to control our will, to weaken it. He knows that a strong and well-oriented will deprives him of any food, any place to stay. He despises the flesh because Jesus took on our flesh and redeemed it. So the devil wants to corrupt our flesh again, to take up residence in our bodies and devour them. He wants to unleash undisciplined passion.
Fasting gives us the chance to exercise and develop our will. That is what we choose when we fast, not pain or distress. The devil flees when the will is properly used, when it is well-practiced.