As long as the flesh is in full health, let us observe abstinence at all times and in every place. When it has been tamed (which I do not suppose is possible this side of the grave), then let us hide our accomplishment.
Stint your stomach and you will certainly lock your mouth, because the tongue is strengthened by an abundance of food. Struggle with all your might against the stomach and restrain it with all sobriety. If you labor a little, the Lord will also soon work with you.
In the eyes of God, it is always preeminently right that a man should spend himself in devising new means for spreading consolation to his subordinates, who are his charges.
Accordingly, a man will neither be puffed up through pride, nor cast down by despair, if he uses the good things divinely bestowed on him, to the glory of the Giver; withholding his desires from the things which he knows will hurt him. And so he that would preserve himself from the wickedness of envy, from the corruption of sensuality, from the unrest of anger, from the desire of revenge, will be purified by the sanctifying power of true abstinence, and will taste the joy of imperishable delights, so that by making spiritual use of them, he will learn to change earthly possessions into heavenly, not by storing what he has received, but by multiplying more and more that which he has been given.
You write that after Communion you felt well. Glory be to God, Who comforts our unworthiness. And as regards the fact that this soon passed, here also is seen His fatherly providence for us. For continual consolation enfeebles the soul and makes it slothful, or leads to even greater harm. That is why the Lord takes it away quickly and again makes us feel our weakness, our helplessness, and our sinfulness. We must humble ourselves more, reproach ourselves, offer repentance for our sins, and not desire consolations, but patiently endure what God allows. Dryness and cooling of fervor are also permitted on account of vainglory.
Just as we must beware of overeating, so too we must beware of excessive temperance or abstinence. Excessive temperance weakens the body, destroys wakefulness, coolness and freshness which are indispensable for vigilance, and which fade and weaken when the physical powers succumb and fail. If you force a weak body to labor beyond its powers, you subject your soul to double darkness, and lead it into confusion (and not relief)...
Without podvig there is altogether no true Christianity, that is to say, Orthodoxy. See what Christ, the First Ascetic, Himself clearly says; 'Whosoever will come after Me, let him deny himself, and take up his cross, and follow Me' (Mark 8:34). The true Christian, the Orthodox Christian, is only he who strives to emulate Christ in the bearing of the cross and is prepared to crucify himself in the Name of Christ. The holy Apostles clearly taught this. Thus the Apostle Peter writes: 'If when you do well and suffer for it, ye take it patiently, this is accepted with God. For even here unto were ye called, because Christ also suffered for us, leaving us an example, that we should follow his steps' (I Pet. 2:2-21). In precisely the same way the holy Apostle Paul says repeatedly in his epistles that all true Christians must be ascetics, and the ascetic labor of the Christian consists of crucifying himself for the sake of Christ: 'They that are Christians have crucified the flesh together with the passions and lusts' (Gal. 5:24). A favorite expression of St. Paul is that we must be crucified with Christ that we might rise with Him.