But if a person is constantly mindful of God, he will rejoice: as the psalmist says, "I remembered God, and I rejoiced" (Psalms 77:3). For when the intellect is gladdened by the remembrance of God, then it forgets the afflictions of this world, places its hope in Him, and is no longer troubled or anxious.
St. Peter of Damaskos, "JOY" (from "The 24 Discourses), "The Philokalia vol. III," - pp. 260 - 263.