3 I would have you draw from your monastic vow not pride but fear. You walk laden with gold; you must keep out of the robber's way. To us men this life is a race-course: we contend here, we are crowned elsewhere. No man can lay aside fear while serpents and scorpions beset his path. The Lord says: “My sword has drunk its fill in heaven,” and do you expect to find peace on the earth? No, the earth yields only thorns and thistles, and its dust is food for the serpent. “For our wrestling is not against flesh and blood, but against the principalities, against the powers, against the world rulers of this darkness, against the spiritual hosts of wickedness in the heavenly places.” We are hemmed in by hosts of foes, our enemies are upon every side.
The weak flesh will soon be ashes: one against many, it fights against tremendous odds. Not till it has been dissolved, not till the Prince of this world has come and found no sin therein, not till then may you safely listen to the prophet's words: “You shall not be afraid for the terror by night nor for the arrow that flies by day; nor for the trouble which haunts you in darkness; nor for the demon and his attacks at noonday. A thousand shall fall at your side and ten thousand at your right hand; but it shall not come near you.” When the hosts of the enemy distress you, when your frame is fevered and your passions roused, when you say in your heart, “What shall I do?”
Elisha's words shall give you your answer, “Fear not, for they that be with us are more than they that be with them.” He shall pray, “Lord, open the eyes of your handmaid that she may see.” And then when your eyes have been opened you shall see a fiery chariot like Elijah's waiting to carry you to heaven, and shall joyfully sing: “Our soul is escaped as a bird out of the snare of the fowlers: the snare is broken and we are escaped.”
Source: Letters (New Advent)