Fasting is supposed to be the ordinary practice of the godly. Christ does not make light of it, but merely cautions them against its abuses.... It is an appendage to prayer, and designed to aid its importunity. It is humbling, and in a manner, chastising ourselves before God.... The spirit of it is expressed in the following passages--"So do God to me and more also, if I taste bread, or aught else, till the sun be down." "Surely I will not come into the tabernacle of my house, nor go up into my bed; I will not give sleep to mine eyes, nor slumber to mine eyelids, until I find out a place for the Lord, an habitation for the mighty God of Jacob." No mention is made of the time, or how often the duty should be attended to.... It is only a means, however; if rested in as an end, it will be an abomination in the sight of God.

Andrew Fuller, qtd. in John Piper, A Hunger for God, p. 191