Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, they have their reward. But thou, when thou fastest, anoint thine head, and wash thy face. Matthew 6:16, 17
The fasting which the word of God enjoins is something more than a form. It does not consist merely in refusing food, in wearing sackcloth, in sprinkling ashes upon the head. He who fasts in real sorrow for sin will never court display. The object of the fast which God calls upon us to keep is not to afflict the body for the sin of the soul, but to aid us in perceiving the grievous character of sin, in humbling the heart before God and receiving His pardoning grace. His command to Israel was, "Rend your heart, and not your garments, and turn unto the Lord your God" (Joel 2:13).
It will avail nothing for us to do penance or to flatter ourselves that by our own works we shall merit or purchase an inheritance among the saints. When the question was asked Christ, "What shall we do, that we might work the works of God?" He answered, "This is the work of God, that ye believe on Him whom He hath sent" (John 6:28, 29). Repentance is turning from self to Christ; and when we receive Christ so that through faith He can live His life in us, good works will be manifest. (Thoughts from the Mount of Blessing, 87)
Reflection: We cannot live a long time without food. It's necessary to sustain life. When we fast, we are telling ourselves--for Christ already knows--that this specific issue is so important that we are willing to forgo food. Hunger pangs remind us over and over again how much we need the Lord in this particular situation.