On Fasting:

Prayer, fasting, vigils, and all other Christian practices, however good they are in themselves, do not constitute the goal of our Christian life, although they serve as a necessary means to its attainment. The true goal of our Christian life consists in the acquisition of the Holy Spirit of God. Fasting, vigils, prayers, alms-giving and all good deeds done for the sake of Christ are but means for the acquisition of the Holy Spirit of God. But note, my son, that only a good deed done for the sake of Christ brings us the fruits of the Holy Spirit. All that is done, if it is not for Christ's sake, although it may be good, brings us no reward in the life to come, nor does it give us God's grace in the present life.

St. Seraphim of Sarov