Chapter XIII. The means by which we can root out dejection from our hearts.
Works of St John Cassian (Institutes, Conferences, On the Incarnation) · Saint John Cassian
We should then be able to expel this most injurious passion from our hearts, so that by spiritual meditation we may keep our mind constantly occupied with hope of the future and contemplation of the promised blessedness. For in this way we shall be able to get the better of all those sorts of dejection, whether those which flow from previous anger or those which come to us from disappointment of gain, or from some loss, or those which spring from a wrong done to us, or those which arise from an unreasonable disturbance of mind, or those which bring on us a deadly despair, if, ever joyful with an insight into things eternal and future, and continuing immovable, we are not depressed by present accidents, or over-elated by prosperity, but look on each condition as uncertain and likely soon to pass away.
Cassian 1.192.2