Blessed are the pure in heart, for they shall see God. Everything we do, our every objective, must be undertaken for the sake of this purity of heart.  This is why we take on loneliness, fasting, vigils, work, nakedness.  For this we must practice the reading of the Scripture, together with all the other virtuous activities, and we do so to trap and to hold our hearts free of the harm of every dangerous passion and in order to rise step by step to the high point of love. (St. John Cassian, + 435, Conferences)

[The Saviour] is hidden in the hearts of those who believe in Him.  They shall see Him and the riches that are in Him when they have purified themselves through love and self-control; and the greater their purity, the more they will see. And that is why He also says, Sell what you possess and give alms (Luke 12:33), and you will find that all things are clean for you (Luke 11:41). This applies to those who no longer spend their time on things to do with the body, but strive to cleanse the intellect (which the Lord calls ‘heart’) from hatred and dissipation. For these defile the intellect and do not allow it to see Christ, who dwells in it by the grace of holy baptism. (St. Maximus the Confessor, + 662, Fourth Century on Love)