The meaning of the Lenten fasting
Fasting is a renewal of the soul, for the holy Apostle says: "Even though our outward man is perishing
Fasting is a renewal of the soul, for the holy Apostle says: "Even though our outward man is perishing, yet the inward is being renewed day by day" (2 Cor 4:16). And if it is being renewed, clearly it is being made beautiful according to its original beauty; made beautiful in itself it is being drawn lovingly to the one who said: "I and the Father will come and make our dwelling with him" (cf. Jn 14:23). If then such is the grace of fasting, that it makes us into a dwelling place of God (cf. Eph 2:22), we must welcome it, brethren, gladly, not grieving at the plainness of the diet, for we know that the Lord, though he is able to nourish lavishly, made a banquet for thousands in the wilderness from bread and water (cf. Mt 14:13-21). Also because what is unusual, with enthusiasm becomes acceptable and painless. Fasting is not defined by foods alone, but by every abstinence from evil, as our godly fathers have explained. And so, I beg you, let us abstain from despondency, idleness, sluggishness, jealousy, strife, maliciousness, self-indulgence, self-reliance; let us abstain from destructive desire which the many-shaped serpent lays before us when we are fasting!
St Theodore the Studite, Small Catecheses 54