Chapter XLIII.--Sleep a Natural Function as Shown by Other Considerations, and by the Testimony of Scripture.
Let us therefore first discuss the question of sleep, and afterwards in what way the soul encounters  death. Now sleep is certainly not a supernatural thing, as some philosophers will have it be, when they suppose it to be the result of causes which appear to be above nature. The Stoics affirm sleep to be "a temporary suspension of the activity of the senses;"  the Epicureans define it as an intermission of the animal spirit; Anaxagoras and Xenophanes as a weariness of the same; Empedocles and Parmenides as a cooling down thereof; Strato as a separation of the (soul's) connatural spirit; Democritus as the soul's indigence; Aristotle as the interruption  of the heat around the heart. As for myself, I can safely say that I have never slept in such a way as to discover even a single one of these conditions. Indeed, we cannot possibly believe that sleep is a weariness; it is rather the opposite, for it undoubtedly removes weariness, and a person is refreshed by sleep instead of being fatigued. Besides, sleep is not always the result of fatigue; and even when it is, the fatigue continues no longer. Nor can I allow that sleep is a cooling or decaying of the animal heat, for our bodies derive warmth from sleep in such a way that the regular dispersion of the food by means of sleep could not so easily go on if there were too much heat to accelerate it unduly, or cold to retard it, if sleep had the alleged refrigerating influence. There is also the further fact that perspiration indicates an over-heated digestion; and digestion is predicated of us as a process of concoction, which is an operation concerned with heat and not with cold. In like manner, the immortality of the soul precludes belief in the theory that sleep is an intermission of the animal spirit, or an indigence of the spirit, or a separation of the (soul's) connatural spirit. The soul perishes if it undergoes diminution or intermission. Our only resource, indeed, is to agree with the Stoics, by determining the soul to be a temporary suspension of the activity of the senses, procuring rest for the body only, not for the soul also. For the soul, as being always in motion, and always active, never succumbs to rest,--a condition which is alien to immortality: for nothing immortal admits any end to its operation; but sleep is an end of operation. It is indeed on the body, which is subject to mortality, and on the body alone, that sleep graciously bestows  a cessation from work. He, therefore, who shall doubt whether sleep is a natural function, has the dialectical experts calling in question the whole difference between things natural and supernatural--so that what things he supposed to be beyond nature he may, (if he likes,) be safe in assigning to nature, which indeed has made such a disposition of things, that they may seemingly be accounted as beyond it; and so, of course, all things are natural or none are natural, (as occasion requires.) With us (Christians), however, only that can receive a hearing which is suggested by contemplating God, the Author of all the things which we are now discussing. For we believe that nature, if it is anything, is a reasonable work of God. Now reason presides over sleep; for sleep is so fit for man, so useful, so necessary, that were it not for it, not a soul could provide agency for recruiting the body, for restoring its energies, for ensuring its health, for supplying suspension from work and remedy against labour, and for the legitimate enjoyment of which day departs, and night provides an ordinance by taking from all objects their very colour. Since, then, sleep is indispensable to our life, and health, and succour, there can be nothing pertaining to it which is not reasonable, and which is not natural. Hence it is that physicians banish beyond the gateway of nature everything which is contrary to what is vital, healthful, and helpful to nature; for those maladies which are inimical to sleep--maladies of the mind and of the stomach--they have decided to be contrariant to nature, and by such decision have determined as its corollary that sleep is perfectly natural. Moreover, when they declare that sleep is not natural in the lethargic state, they derive their conclusion from the fact that it is natural when it is in its due and regular exercise. For every natural state is impaired either by defect or by excess, whilst it is maintained by its proper measure and amount. That, therefore, will be natural in its condition which may be rendered non-natural by defect or by excess. Well, now, what if you were to remove eating and drinking from the conditions of nature? if in them lies the chief incentive to sleep. It is certain that, from the very beginning of his nature, man was impressed with these instincts (of sleep).  If you receive your instruction from God, (you will find) that the fountain of the human race, Adam, had a taste of drowsiness before having a draught of repose; slept before he laboured, or even before he ate, nay, even before he spoke; in order that men may see that sleep is a natural feature and function, and one which has actually precedence over all the natural faculties. From this primary instance also we are led to trace even then the image of death in sleep. For as Adam was a figure of Christ, Adam's sleep shadowed out the death of Christ, who was to sleep a mortal slumber, that from the wound inflicted on His side might, in like manner (as Eve was formed), be typified the church, the true mother of the living. This is why sleep is so salutary, so rational, and is actually formed into the model of that death which is general and common to the race of man. God, indeed, has willed (and it may be said in passing that He has, generally, in His dispensations brought nothing to pass without such types and shadows) to set before us, in a manner more fully and completely than Plato's example, by daily recurrence the outlines of man's state, especially concerning the beginning and the termination thereof; thus stretching out the hand to help our faith more readily by types and parables, not in words only, but also in things. He accordingly sets before your view the human body stricken by the friendly power of slumber, prostrated by the kindly necessity of repose immoveable in position, just as it lay previous to life, and just as it will lie after life is past: there it lies as an attestation of its form when first moulded, and of its condition when at last buried--awaiting the soul in both stages, in the former previous to its bestowal, in the latter after its recent withdrawal. Meanwhile the soul is circumstanced in such a manner as to seem to be elsewhere active, learning to bear future absence by a dissembling of its presence for the moment. We shall soon know the case of Hermotimus. But yet it dreams in the interval. Whence then its dreams? The fact is, it cannot rest or be idle altogether, nor does it confine to the still hours of sleep the nature of its immortality. It proves itself to possess a constant motion; it travels over land and sea, it trades, it is excited, it labours, it plays, it grieves, it rejoices, it follows pursuits lawful and unlawful; it shows what very great power it has even without the body, how well equipped it is with members of its own, although betraying at the same time the need it has of impressing on some body its activity again. Accordingly, when the body shakes off its slumber, it asserts before your eye the resurrection of the dead by its own resumption of its natural functions. Such, therefore, must be both the natural reason and the reasonable nature of sleep. If you only regard it as the image of death, you initiate faith, you nourish hope, you learn both how to die and how to live, you learn watchfulness, even while you sleep.