St. Diadochus of Photiki: On Baptism and the Remembrance of God

 Before holy baptism grace encourages the soul towards good from the outside, while Satan lurks in its depths, trying to block all the intellect's ways of approach to the divine. But from the moment that we are reborn through Baptism, the demon is outside, grace is within...

It is a mark of one who truly loves holiness that he continually burns up what is worldly in his heart through practicing the remembrance of God, so that little by little evil is consumed in the fire of this remembrance and his soul completely recovers its natural brilliance with still greater glory.

+St. Diadochus of Photiki, from One Hundred Texts on Spiritual Knowledge and Discernment, The Philokalia, Volume 1

St. Anatoly of Optima, Saving Temptations

Pride is the culmination of the demonic scheme. But He "Who will have all men to be saved and to come unto the knowledge of the truth"(1 Timothy 2:4) permits the Devil and people to humble us... Since, Matushka, in God's first blessed instrument intended for your healing you do not wish to recognize God's hand, therefore temptations are sent to you... If you are not made wiser, yet more temptations or afflictions will be sent to you, greater than the first. (c.f. St. Mark the Ascetic, "On the Spiritual Law", #46, Philokalia 1)  But let us hasten to humble ourselves, let us endure patiently, guarding ourselves with the fear of God...
+St. Anatoly (Zertsalov) of Optina, from A Collection of Letters to Nuns, Profitable instructions for laymen and monastics, letter 43, Saving Temptations

St. Joseph the Hesychast: Who has conquered the devil?

Who has conquered the devil? He who knows his own weaknesses, passions, and shortcomings. Whoever is afraid of knowing himself remains far from knowledge, and he doesn't love anything else except seeing faults in others and judging them. He doesn't see gifts in other people, but only shortcomings. And he doesn't see his own shortcomings, but only his gifts. This is truly the sickness that plagues us men of the eighth millenium (Ps 24:18, LXX): we fail to recognize one another's gifts.

+ St. Joseph the Hesychast from Monastic Wisdom, The Letters of Elder Joseph the Hesychast.