Here is another excerpt from the Philokalia which might be helpful, this one by St. John Cassian:
"Our eighth struggle is against the demon of pride, a most sinister demon, fiercer than all that have been discussed up till now. He attacks the perfect above all and seeks to destroy those who have mounted almost to the heights of holiness. Just as a deadly plague destroys not just one member of the body, but the whole of it, so pride corrupts the whole soul, not just part of it. Each of the other passions that trouble the soul attacks and tries to overcome the single virtue which is opposed to it, and so darkens and troubles the soul only partially. But the passion of pride darkens the soul completely and leads to its utter downfall.
In order to understand more fully what is meant by this, we should look at the problem in the following way. Gluttony tries to destroy self-control; unchastity, moderation; avarice, voluntary poverty; anger, gentleness; and the other forms of vice, their corresponding virtues. But when the vice of pride has become master of our wretched soul, it acts like some harsh tyrants who has gained control of a great city, and destroys it completely, razing it to its foundations. The angel who fell from heaven because of his pride bears witness to this. He had been created by God and adorned with every virtue and all wisdom, but he did not want to ascribe this to the grace of the Lord. He ascribed it to his own nature and as a sresult regarded himself as equal to God. The prophet rebukes this claim when he says: 'You have said in your heart: "I will sit on a high mountain; I will place my throne upon the clouds and I will be like the Most High." Yet you are a man, and not God' (cf Is. 14:13-14).
And again, another prophet says, 'Why do you baost of your wickedness, O mighty man?' and he continues in this same vein (Ps. 52:1). Since we are aware of this we should feel fear and guard our hearts with extreme care from the deadly spirit of pride. When we have attained some degree of holiness we should always repeat to ourselves the words of the Apostles: 'Yet not I, but the grace of God which was with me' (1 Cor. 15:10), as well as what was said by the Lord: 'Without Me you can do nothing' (John 15:5). We should also bear in mind what the prophet said: 'Unless the Lord builds the house, they labour in vain that build it' (Ps. 127:1), and finally: 'It does not depend on man's will or effort, but on God's mercy' (Rom. 9:16).
Even if someone is sedulous, serious and resolute, he cannot, so long as he is bound to flesh and blood, approach perfection except through the mercy and grace of Christ. James himself says that 'every good gift is from above' (James 1:17), while the Apostles Paul asks: 'What do you have which you did not receive? Now if you received it, why do you boast, as if you had not received it?' (1 Cor. 4:7) What right, then, has man to be proud as though he could achieve perfection through his own efforts?
The thief who received teh kingdom of heaven, though not as the reward of virtue, is a true witness to the fact that salvation is ours through the grace and mercy of God. All of our holy fathers knew this and all with one accord teach that perfection in holiness can be achieved only through humility. Humility, in its turn, can be achieved only through faith, fear of God, gentleness and the shedding of all possessions. It is by means of these that we attain perfect love, through the grace and compassion of our Lord Jesus Christ, to whom be glory through all the ages. Amen."
--Edited by G.E.H. Palmer, Philip Sherrard, Kallistos Ware, The Philokalia: The Complete Text, Volume 1, (Faber and Faber, 1979), pp. 92-93