The Holy Prophet said, 'Fasting is a protection from the calamities of this world, and a veil from punishment of the next.' When you fast, intend thereby to restrain yourself from fleshly appetites and to cut off those worldly desires arising from the ideas of Satan and his kind. Put yourself in the position of a sick person who desires neither food nor drink; expect recovery at any moment from the sickness of wrong actions. Purify your inner being of every lie, turbidity, heedlessness and darkness, which might cut you off from the meaning of being sincere for the sake of Allah.
Somebody said to one of the Companions, 'You are already weak; fasting will weaken you further.' 'I am preparing that fast for the evil of a long day,' he said. 'Patience in obeying Allah is easier than patience in His punishment.' And the Messenger of Allah once quoted Allah's words, 'Fasting is done for Me, and I am its reward.'
Fasting kills the desire of the self and the appetite of greed, and from it comes purity of the heart, purification of the limbs, cultivation of the inner and the outer being, thankfulness for blessings, charity to the poor, increase of humble supplication, humility, weeping and most of the ways of seeking refuge in Allah; and it is the reason for the breaking of aspiration, the lightening of evil things, and the redoubling of good deeds. It contains benefits which cannot be counted. It is enough that we mention some of them to the person who understands and is given success in making use of fasting, if Allah wills.