Cardinal Manning explains the fifth effect of venial sin: “Just as a small ailment may become a mortal sickness, so a venial sin may become a mortal sin, and that with great facility. Not that any number of venial sins, if they be heaped together, would make a mortal sin; because, as I have shown you from the first, mortal sins consist in their malice, and venial sins are without this deliberate malice; but they may put off their character and stature of venial sins, and they may put on the character and rise to the stature of deadly sins. This they do in five ways.”
“First of all, a venial sin may be committed with the intention of covering or accomplishing some mortal sin, and then it is mortal too.” For example: “Suppose a man to tell a lie in a very light matter—some little deceit. He is asked, ‘Is such a one in this place?’ He answers, ‘No,’ because he intends thereby to cover and to commit a mortal sin. The two sins then become one.”
“Or secondly, it may be committed with a consciousness that it will certainly lead to a mortal sin, and yet nevertheless is persevered in.” For example: “If I take a book—some book of levity which may not in itself be positively wrong—I begin to read it on a Sunday morning, and I am determined I will finish it; and I know that in half-an-hour it is my duty to go to Holy Mass. . . . Nevertheless I go on reading, indulging myself, disregarding my duty, until at last I turn my back on our Divine Lord.”
“Or thirdly, it may be done with a knowledge of God’s prohibition, with an open-eyed consciousness, and out of contempt of just authority.”
“Or fourthly, it may be so publicly and notoriously done, as to give scandal to others, and to encourage and invite them to commit grave sin.”
“Or lastly, it may be done in the proximate peril of falling into mortal sin, and that with our eyes open; and thus to expose ourselves to mortal sin is mortal in itself.”
Quotations from Henry Edward Manning, Sin and Its Consequences, 2d ed. (London: Burns and Oates, 1874).