Letter 1
16 For this reason also the devil, knowing that they who have committed great evils, when they have begun to repent, do this with much zeal, inasmuch as they are conscious of their offenses, fears and trembles lest they should make a beginning of the work; for after they have made it they are no longer capable of being checked, and, kindling like fire under the influence of repentance, they render their souls purer than pure gold, being impelled by their conscience, and the memory of their former sins, as by some strong gale, towards the haven of virtue.
And this is the point in which they have an advantage over those who have never fallen, that they exercise more vehement energy; if only, as I said, they can lay hold of the beginning. For the task which is hard and difficult of accomplishment is to be able to set foot on the entrance, and to reach the vestibule of repentance, and to repulse and overthrow the enemy there when he is fiercely raging and assaulting us. But after this, he will not display so much fury when he has once been worsted, and has fallen where he was strong, and we shall receive greater energy, and shall run this good race with much ease.
Let us then in future set about our return, let us hasten up to the city which is in Heaven, in which we have been enrolled, in which also we have been appointed to find our home as citizens. For to despair of ourselves not only has this evil that it shuts the gates of that city against us, and that it drives us into greater indolence and contempt, but also that it plunges us into Satanic recklessness. For the only cause why the devil became such as he is was that he first of all despaired, and afterwards from despair sank into recklessness.
For the soul, when once it has abandoned its own salvation, will no longer perceive that it is plunging downwards, choosing to do and say everything which is adverse to its own salvation. And just as madmen, when once they have fallen out of a sound condition, are neither afraid nor ashamed of anything, but fearlessly dare all manner of things, even if they have to fall into fire, or deep water, or down a precipice; so they who have been seized by the frenzy of despair are hence forward unmanageable, rushing into vice in every direction, and if death does not come to put a stop to this madness, and vehemence, they do themselves infinite mischief.
Therefore I entreat you, before you are deeply steeped in this drunkenness, recover your senses and rouse yourself up, and shake off this Satanic fit, doing it gently and gradually if it be not possible to effect it all at once. For to me indeed the easier course seems to be to wrench yourself once for all out of all the cords which hold you down, and transfer yourself to the school of repentance. But if this seems to you a difficult thing, that you should be willing to enter on the path which leads to better things, simply enter upon it, and lay hold on eternal life.
Yea, I beseech and implore you by your former reputation, by that confidence which once was yours, let us see you once again standing on the pinnacle of virtue, and in the same condition of perseverance as before. Spare those who are made to stumble on your account, those who are falling, who are becoming more indolent, who are despairing of the way of virtue. For dejection now holds possession of the band of brethren, while pleasure and cheerfulness prevail in the councils of the unbelieving, and of those young men who are disposed to indolence.
But if you return again to your former strictness of life the result will be reversed, and all our shame will be transferred to them, while we shall enjoy much confidence, seeing you again crowned and proclaimed victor with more splendour than before. For such victories bring greater renown and pleasure. For you will not only receive the reward of your own achievements, but also of the exhortation and consolation of others, being exhibited as a striking model, if ever any one should fall into the same condition, to encourage him to get up and recover himself.
Do not neglect such an opportunity of gain, nor drag our souls down into Hades with sorrow, but let us breathe freely again, and shake off the cloud of despondency which oppresses us on your account. For now, passing by the consideration of our own troubles, we mourn over your calamities, but if you are willing to come to your senses, and see clearly, and to join the angelic host, you will release us from this sorrow, and will take away the greater part of sins. For that it is possible for those who have come back again after repentance to shine with much lustre, and oftentimes more than those who have never fallen at all, I have demonstrated from the divine writings.
Thus at least both the publicans and the harlots inherit the kingdom of Heaven, thus many of the last are placed before the first.
Source: Two Letters to Theodore After His Fall (New Advent)