The Conferences Of John Cassian by John Cassian
Chapter XIV. An objection, that the saying: |For I do not the good that I would,| etc., applies to the persons neither of unbelievers nor of saints.
Germanus: We say that this does not apply to the persons either of those who are involved in capital offences, or of an Apostle and those who have advanced to his measure, but we think that it ought properly to be taken of those who after receiving the grace of God and the knowledge of the truth, are anxious to keep themselves from carnal sins but, as ancient custom like a natural law rules most forcibly in their members, they are carried away to the ingrained lust of their passions. For the custom and frequency of sinning becomes like a natural law, which, implanted in the man's weak members, leads the feelings of the soul that is not yet instructed in all the pursuits of virtue, but is still, if I may say so, of an uninstructed and tender chastity, captive to sin and subjecting them by an ancient law to death, brings them under the yoke of sin that rules over them, not suffering them to obtain the good of purity which they love, but rather forcing them to do the evil which they hate.