Peter was first given the keys, but then he was allowed to fall into the sin of denying Christ; and so his pride was humbled by his fall. Do not be surprised, then, if after receiving the keys of spiritual knowledge you fall into various evil thoughts. Glorify our Lord, for He alone is wise: through setbacks of this kind He restrains the presumption that we tend to feel because of our advance in the knowledge of God. Trials and temptations are the reins whereby God in His providence restrains our human arrogance.
According to St. Gregory the Sinaite there are three degrees in eating: temperance, sufficiency, and satiety. Temperance is when someone wants to eat some more food but abstains, rising from the table still somewhat hungry. Sufficiency is when someone eats what is needed and sufficient for normal nourishment. Satiety is when someone eats more than enough and is more than satisfied. Now if you cannot keep the first two degrees and you proceed to the third, then, at least, do not become a glutton, remembering the words of the lord: 'Woe unto you that are full now, for you shall hunger' (Lk. 6:25). Remember also that rich man who ate in this present life sumptuously every day, but who was deprived of the desired bosom of Abraham in the next life, simply because of this sumptuous eating.
We believe that the divine presence is everywhere and that 'the eyes of the Lord are looking on the good and the evil in every place.' But we should believe this especially without any doubt when we are assisting at the Work of God. To that end let us be mindful always of the Prophet's words, 'Serve the Lord in fear' and again, 'Sing praises wisely' and 'In the sight of the Angels I will sing praise to Thee.' Let us therefore consider how we ought to conduct ourselves in the sight of the Godhead and of His Angels, and let us take part in the psalmody in such a way that our mind may be in harmony with our voice.
One should not ponder divine matters on a full stomach, say the ascetics. For the well-fed, even the most superficial secrets of the Trinity lie hidden.
'Then the devil left Him, and angels came and ministered to Him' (Matthew 4:11). It does not say that the angels were with our Lord during the actual time when He was being tempted. In the same way, when we are being tempted, God's angels for a time withdraw a little. Then, after the departure of those tempting us, they come and minister to us with divine intellections, giving us support, illumination, compunction, encouragement, patient endurance, joyfulness, and everything that saves and strengthens and renews our exhausted soul. As Nathaniel was told, 'You will see the angels ascending and descending upon the Son of man' (John 1:51); in other words, the ministry and assistance of the angels will be given generously to mankind.
The best medicine for pride, man’s greatest sickness of soul, is humility. Words cannot describe or explain it, but the Fathers say that he who strives hard to live according to the precepts of our Lord, and is fully aware of his own sins, acquires it steadily. Therefore be very careful never to think yourself good, or the least bit better than others.
Therefore we must not grow weary. We must be steadfast, immovable, always abounding in the work of the Lord, knowing that in the Lord our labor is not in vain (I Corinthians 15:58). Having once begun, we must not cease to perform deeds worthy of our repentance. To rest is the same as to retreat.
Spiritual activity embodies Christ in our soul. This involves continual remembrance of the Lord: you hide Him within, in your soul, your heart, your consciousness.
Our achievements must never loom large in our eyes; only our failures. But this must never lead us to despondency - the constant temptation - only to humility.
He stands, then - but not alone, for before Him go angels, saying: 'Lift up the gates, O ye the princes.' What gates? Even those of which the Psalmist sings in another place also: 'Open to me the gates of righteousness.' Open, then, thy gates to Christ, that He may come into thee - open the gates of righteousness, the gates of chastity, the gates of courage and wisdom. Believe the message of the angels: 'Be ye lifted up, ye everlasting doors, and the King of Glory shall come in, the Lord of Sabaoth.'
Think also of this: the person who is bound to earthly things may rejoice but may also be upset or disturbed or grieved over earthly things: his mind is exposed to continual changes. But the joy of your master (Matthew 25:21) is enduring, for God is unchangeable. Thus control your tongue at the same time as you discipline your body with fasting and strictness. Talkativeness is a great enemy of prayer. A spate of fluttering words stands in the way of the words of prayer. This is the reason that we shall render account for every careless word we utter (Matthew 12:36). One does not bring the dust of the road into a room that one wishes to keep clean; thus keep your heart free from gossip and chatter about the events of the day that is past.
Remember always that, once we have decided consciously to strive after righteousness, we cannot escape catastrophes and sorrows, no matter where we are.
The humility which in due time and by God's grace, after many struggles and tears, is given by heaven to those who seek it is something incompararably stronger and higher than the sense of abasement felt by those who have lapsed from holiness. This higher humility is granted only to those who have attained true perfection and are no longer under the sway of sin.
By the death of martyrs religion has been defended, faith increased, the Church strengthened; the dead have conquered, the persecutors have been overcome. And so we celebrate the death of those of whose lives we are ignorant. So, too, David rejoiced in prophecy at the departure of his own soul, saying: 'Precious in the sight of the Lord is the death of His saints.' He esteemed death better than life. The death itself of the martyrs is the prize of their life. And again, by the death of those at variance hatred is put an end to.
You ask for some way of completely eradicating irritability. The inclination to irritability is given us to use against sin, and we were never meant to use it against our fellow men. When we do, we act contrary to our true nature.