St. Ignatius Brianchaninov: The gift of prayer

The gift [of prayer] is given to those who humble and abase themselves before the greatness of the gift. The gift is given to those who renounce their own will and surrender themselves to the will of God. The gift is given to those who subdue and mortify their flesh and blood, who subdue and mortify the mind of the flesh by the commandments of the Gospel. Life dawns and rises according to the degree of our mortification. It comes unexpectedly, entirely at its own good pleasure, and then it completes and perfects the mortification begun voluntarily. Careless, especially self-willed proud and self-directed seekers of a high state of prayer are always sealed with the seal of rejection with the precision of spiritual law (Matt 22:12-14). The removal of that seal is very difficult, mostly impossible. Why? Because pride and self-confidence which leads to self-deception, to fellowship with demons and enslavement of them, do not allow us to see the wrongness and peril of our positions, do not allow us to see our woeful fellowship with the demons, nor our disastrous, fatal enslavement to them. "Clothe yourself first with leaves, and then when God commands bring the fruits."¹ said the fathers. First acquire attentive prayer. To one purified and prepared by attentive prayer, trained and qualified by the commandments of the Gospel and grounded on them, God - the all-merciful God - will give in His time the prayer of Grace.
+St. Ignatius Brianchaninov, from On the Prayer of Jesus, The Method of St. John of the Ladder

¹ St. Barsanuphius the Great and John the Prophet, Letters, Volume 1, Answer 325.