Not nakedness, not platted hair, not dirt, not fasting, or lying on the earth, not rubbing with dust, not sitting motionless, can purify a mortal who has not overcome desires. [Dhammapada 10.141].
Often we strive to attain lofty spiritual states by physical efforts. Being accustomed to the cause and effect models of material existence, we assume this methodology extends into the spiritual realm. We think we can accumulate piety by adorning ourselves with spiritual costumes, attending religious ceremonies and quoting a few passages of scripture.
That makes little sense when we forget to sublimate our intentions and fail to purify our thoughts. In other words, striving for lofty spiritual states to satisfy base physical desires such as ego, pride, fame or other common human ambitions, is incongruous with Divine service. Such efforts may attain material benefits, but they do not achieve greater spiritual consciousness.
. . . when exercised with a pure heart and a right motive, fasting may provide us with a key to unlock doors where other keys have failed; a window opening up new horizons in the unseen world; a spiritual weapon of God’s provision, mighty, to the pulling down of strongholds. [Arthur Wallis, God’s Chosen Fast (Kingsway: 1968)].
Human beings can corrupt almost anything, no matter how good or sacred its origin and purpose. We can easily image goodness, kindness and mercy being abused and perverted for selfish gain and greedy advantage. It should not come as a surprise that some aspects of fasting require caution and restraint.
As with any act worship, fasting can become an empty ritual devoid of piety and sincerity. Negative thoughts, hypocritical behavior, anger and pride can all infect our abstinence.
Perhaps the most dangerous aspect of fasting is that it can become a personal ambition, a mental objective to be attained for selfish desires. In other words, a person who initially fasts for pious, spiritual reasons may become so gratified with abstaining from food that the act, itself, develops into a goal. The physical accomplishment of not eating replaces the spiritual goal of seeking God consciousness.
This is, in fact, the common danger that runs through all spiritual practices. We similarly encounter it in persons who pray or give in charity merely to be seen and admired by others. We see it in the spiritual leader who haughtily exults in his religious knowledge and in his position over the congregation. He becomes proud and arrogant and thereby loses all that he has gained.
Such debilitating results occur when we reduce the purpose of the fast to worldly ends. We may experience many physical and material benefits from fasting, but ultimately we must be seeking God.
The fact that God exists and that fasting heightens this awareness must remain paramount. Fasting should not become another idol on the altar of the material world.
In order to preserve the mind and body in a perfect condition, abstinence from food is not alone sufficient: unless the other virtues of the mind as well are joined to it . . . And so humility must first be learned . . . anger should be controlled . . . vainglory should be despised, the disdainfulness of pride trampled under foot, and the shifting and wandering thoughts of the mind restrained by continual recollection of God. [John Cassian, The Training of a Monk and the Eight Deadly Sins, Of the Spirit of Gluttony. (The Book of Fasts and Abstinence) Chapter X]