St John is famous for his "tangents". He is here commenting on "So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do." (Luke 17:10). This is in the middle of a sermon on the genealogy at the beginning of St Matthew!
St John's tangents are always practical and moral in nature. Here he gives marvelous advice which we should all be careful to keep.
At the end of this letter will be a large excerpt from St. John's sermon. It is a little difficult to read, because the English is archaic, but the meaning of the small bit I have put at the top of this letter should be clear to the Christian.
Basically, summing it up, if you want to be freed from your passions and achieve peace, then be humble. May God help us to be humble, and realize that peace which Christ came to give us.
So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do. (Luke 17:10)
8. Let us beware therefore of saying anything about ourselves, for this renders us both odious with men and abominable to God. For this reason, the greater the good works we do, the less let us say of ourselves; this being the way to reap the greatest glory both with men and with God. Or rather, not only glory from God, but a reward, yea, a great recompense.
Demand not therefore a reward that thou mayest receive a reward.
Confess thyself to be saved by grace, that He may profess Himself a debtor to thee; and not for thy good works only, but also for such rightness of mind. For when we do good works, we have Him debtor for our good works only; but when we do not so much as think we have done any good work, then also for this disposition itself; and more for this, than for the other things: so that this is equivalent to our good works. For should this be absent, neither will they appear great.
For in the same way, we too, when we have servants, do then most approve them when, after having performed all their service with good will, they do not think they have done anything great.
Wherefore, if thou wouldest make thy good deeds great, do not think them to be great, and then they will be great.
It was in this way that the centurion also said, “I am not fit that thou shouldest enter under my roof;” because of this, he became worthy, and was “marvelled at” (Matt. viii. 8) above all Jews.
On this wise again Paul saith, “I am not meet to be called an apostle;”(1 Cor. xv. 9) because of this he became even first of all.
So likewise John: “I am not meet to loose the latchet of His shoe;”(Mark i. 7; Luke iii. 16; John i. 27, iii). 29. because of this he was the “friend of the Bridegroom,” and the hand which he affirmed to be unworthy to touch His shoes, this did Christ draw unto His own head.
So Peter too said, “Depart from me, for I am a sinful man;”(Luke v. 8) because of this he became a foundation of the Church.
For nothing is so acceptable to God as to number one’s self with the last. This is a first principle of all practical wisdom.
will not be vainglorious,
will not be wrathful,
will not envy his neighbor,
will not harbor any other passion.
For neither when a hand is bruised, though we strive ten thousand times, shall we be able to lift it up on high. If therefore we were thus to bruise our heart likewise, though it were stirred by ten thousand swelling passions, it could not be lifted up, no, not ever so little. For if a man, by mourning for things pertaining to this life, drives out all the diseases of his soul, much more will he, who mourns for sins, enjoy the blessing of self-restraint.
http://www.ccel.org/ccel/schaff/npnf110.iii.vi.html NPNF1-10. St. Chrysostom: Homilies on the Gospel of Saint Matthew, Homily 3