A Treatise On The Soul by Tertullian
Chapter XLI.--Notwithstanding the Depravity of Man's Soul by Original Sin, There is Yet Left a Basis Whereon Divine Grace Can Work for Its Recovery by Spiritual Regeneration.
There is, then, besides the evil which supervenes on the soul from the intervention of the evil spirit, an antecedent, and in a certain sense natural, evil which arises from its corrupt origin. For, as we have said before, the corruption of our nature is another nature having a god and father of its own, namely the author of (that) corruption. Still there is a portion of good in the soul, of that original, divine, and genuine good, which is its proper nature. For that which is derived from God is rather obscured than extinguished. It can be obscured, indeed, because it is not God; extinguished, however, it cannot be, because it comes from God. As therefore light, when intercepted by an opaque body, still remains, although it is not apparent, by reason of the interposition of so dense a body; so likewise the good in the soul, being weighed down by the evil, is, owing to the obscuring character thereof, either not seen at all, its light being wholly hidden, or else only a stray beam is there visible where it struggles through by an accidental outlet. Thus some men are very bad, and some very good; but yet the souls of all form but one genus: even in the worst there is something good, and in the best there is something bad. For God alone is without sin; and the only man without sin is Christ, since Christ is also God. Thus the divinity of the soul bursts forth in prophetic forecasts in consequence of its primeval good; and being conscious of its origin, it bears testimony to God (its author) in exclamations such as: Good God! God knows! and Good-bye! Just as no soul is without sin, so neither is any soul without seeds of good. Therefore, when the soul embraces the faith, being renewed in its second birth by water and the power from above, then the veil of its former corruption being taken away, it beholds the light in all its brightness. It is also taken up (in its second birth) by the Holy Spirit, just as in its first birth it is embraced by the unholy spirit. The flesh follows the soul now wedded to the Spirit, as a part of the bridal portion -- no longer the servant of the soul, but of the Spirit. O happy marriage, if in it there is committed no violation of the nuptial vow!