From The Way of a Pilgrim:
So with the object of helping this brother and doing all I could to strengthen his faith, I took The Philokalia out of my knapsack. Turning to the 109th chapter of Isikhi, I read it to him. I set out to prove to him the uselessness and vanity of avoiding sin merely from fear of the tortures of hell. I told him that the soul could be freed from sinful thoughts only by guarding the mind and cleansing the heart, and that this could only be done by interior prayer. I added that according to the holy Fathers, one who performs saving works simply from the fear of hell follows the way of bondage, and he who does the same just in order to be rewarded with the kingdom of heaven follows the path of a bargainer with God. The one they call a slave, the other a hireling. But God wants us to come to Him as sons to their Father; He wants us to behave ourselves honorably from love for Him and zeal for His service; He wants us to find our happiness in uniting ourselves with Him in a saving union of mind and heart.