Saint Gregory of Sinai. "On Commandments and Doctrines, Warnings and Promises; On Thoughts, Passions and Virtues, and Also on Stillness and Prayer: One Hundred and Thirty-Seven Texts". From Philokalia, Vol. 4.
115. Those who say or do anything without humility are like people who build in winter or without bricks and mortar. Very few acquire humility and know it through experience; and those who try to talk about it are like people measuring a bottomless pit. And I who in my blindness have formed a faint image of this great light am rash enough to say this about it: true humility does not consist in speaking humbly, or in looking humble. The humble person does not have to force himself to think humbly, nor does he keep finding fault with himself. Such conduct may provide us with an occasion for humility or constitute its outward form, but humility itself is a grace and a divine gift. The holy fathers teach that there are two kinds of humility: to regard oneself as lower than everyone else, and to ascribe all one's achievement to God. The first is the beginning, the second the consummation.
Those who seek humility should bear in mind the three following things: that they are the worst of sinners, that they are the most despicable of all creatures since their state is an unnatural one, and that they are even more pitiable than the demons, since they are slaves to the demons. You will also profit if you say this to yourself: how do I know what or how many other people's sins are, or whether they are greater than or equal to my own? In our ignorance you and I, my soul, are worse than all men, we are dust and ashes under their feet. How can I not regard myself as more despicable than all other creatures, for they act in accordance with the nature they have been given, while I, owing to my innumerable sins, am in a state contrary to nature. Truly animals are more pure than I, sinner that I am; on account of this I am the lowest of all, since even before my death I have made my bed in hell. Who is not fully aware that the person who sins is worse than the demons, since he is their thrall and their slave, even in this life sharing their murk-mantled prison? If I am mastered by the demons I must be inferior to them.
Therefore my lot will be with them in the abyss of hell, pitiful that I am. You on earth who even before your death dwell in that abyss, how do you dare delude yourself, calling yourself righteous, when through the evil you have done you have defiled yourself and made yourself a sinner and a demon? Woe to your self-deception and your delusion, squalid cur that you are, consigned to fire and darkness for these offences.