The soul is something incorporeal, capable of reason, destined to impart life to the body. It is this which makes men animal, acquainted with the things of the flesh, cleaving to bodily sensation. But when it begins to be not only capable but also in possession of perfect reason, it immediately renounces the mark of the feminine and becomes spirit endowed with reason, fitted to rule the body, spirit in possession of itself. For as long as it is soul it is quick to slip effeminately into what is of the flesh; but the spirit thinks only on what is virile and spiritual.

            Man’s spirit was created wih an acute perception in the quest for good and with an active nature. In the womb of creative Wisdom it excelled every material object, shone brighter than all bodily light, and was of greater dignity because it was the image of its Creator and capable of reason. But it was implicated in the fault attached to its fleshly origin and made the slave of sin, taken captive by the law of sin which is in its members.

            Yet it did not wholly lose its power of choice, that is, the power of the reason to judge and to discern, although it lost its freedom to will and to act. For as a punishment for sin and as evidence of the natural dignity it had lost, the power of choice was left to it, although captive, as a sign. This even before the conversion and liberation of the will it can never wholly lose by any perversion of the will. Even when it abuses this power to choose evil instead of good, it is, as has been said, better and of greater dignity than any bodily creature, both in itself and in the womb of creative Wisdom

            Now the will is set free when it becomes charity: when the charity of God is poured out in our hearts by the Holy Spirit who is given to us. And then reason is truly reason, that is a disposition of the mind ready to conform to the truth in all things. For when the will has been set free by liberating grace and the spirit begins to be moved by a reason that is free, then it becomes its own master, that is, it makes free use of itself; it becomes spirit and a good spirit. Spirit insofar as it imparts life well and brings its animal part to fultillment by the addition of the ability to reason freely; good in sofar as it now loves its good by which it becomes good and without which it could be neigher good nor spirit.

            Man endowed with spirit becomes good and rational, loving the Lord his God with his whole heart and his whole sould and all his mind and all his strength, and, only in God, himself and his neighbor as himself. He has the good spirit which fears God and keeps his commandment: this is the whole of man.

–  William of St. Thierry, The Golden Epistle Book Two IV –