Cardinal Manning explains that for a sin to be mortal, and not merely venial, “it is necessary that there should be a gravity in the matter of the sin; and the gravity of that matter will be constituted in one of two ways—it is either the material gravity, that is, the extent, or amount, or quantity of the sin committed; or it is the moral gravity derived from the circumstances of the case.” He offers this illustration:
“If I were to rob a man of a very large amount of his property, no one would doubt for an instant that I had committed a sin unto death, or a mortal sin. The common sense of mankind, the instincts of justice, would at once pronounce against me. If I were to take a needle from some rich person, the instincts of justice would acquit me of a sin unto death. I have taken that which did not belong to me, but no one would say that, in taking that needle from the rich man, who could obtain an abundant supply of needles, I had committed a sin unto death.”
“But suppose that needle belonged to a poor seamstress, who gained her daily bread by the industrious use of that one needle, and that she had not the means to buy another; and that if she were robbed of it, her industry must cease, and she could no longer gain her bread; and that I knew all those facts; and that, with my eyes open, knowing the extent of the injury I was doing, in violation of the law of charity, as well as of the law of justice, I should take that needle with a perfect consciousness that I was destroying the means of industry and reducing her to hunger. You see at once that there is a moral guilt which arises from these circumstances. Suppose, still further, that I myself were jealous of her prosperity, being of the same trade or calling, and that I take the needle in order to ruin her for my own advantage. You see, therefore, that in so small a theft as the stealing of a needle there may be an enormity of moral guilt.”
“It is not enough then that there should be the knowledge of the intellect, and the consent of the will to the action, unless the matter in which that action is committed shall be of a grave kind, either materially or morally, before God.”
Quotations from Henry Edward Manning, Sin and Its Consequences, 2d ed. (London: Burns and Oates, 1874).