St Seraphim of Sarov writes on despair: ‘As the Lord works for our salvation, so the devil, that killer of men, works to lead man into despair.’ Judas the betrayer was little of soul and untested in battle, and therefore the devil, seeing him in despair, attacked him and forced him to suicide. But Peter, the firm rock, when he fell into great sin in the testing time of battle, did not despair nor lose the presence of the Spirit, but wept bitterly from a full heart, and the devil seeing this, fled from him as from a flaming fire. And, my brethren, St Antiochus teaches that, when despair descends upon us, we must not surrender to it but, strengthened and protected by our holy Faith, say resolutely to the wicked spirit: ‘What hast thou to do with us, thou who hast fallen away from God, thou fugitive from heaven and slave of wickedness? Thou darest in no wise do us harm, for Christ the Son of God has dominion over us and over all. But thou, O thou murderer, get thee away from us! Strengthened by His precious Cross, we trample upon thy serpent head!’
Source:
Bishop St Nikolai Velimirovic, Prologue from Ochrid
St Vasilios Greek Orthodox Church 