The approved authors of the moral books had much to say about the administration of the sacraments and about the minister's moral responsibility regarding the duty to administer and refuse the sacraments to certain persons. They were concerned with a few different principles and precepts which helped to clarify the role of the minister as one who acts in the name of Christ. "The sacraments were instituted by Christ as so many channels or conduits by which he might convey to the souls of men the fruits of his passion and death. They are administered in his name and by his authority, and so Christ himself is the principal minister of the sacraments." (Thomas Slater, S.J., A Manual of Moral Theology for English-Speaking Countries, Vol. 2 [New York: Benziger, 1925] 61.) The concern for the proper administration of the sacraments was manifested clearly in the treatment of the responsibilities of the minister.
Recently, however, in any number of statements made by those who do not support withholding of the sacrament of the Holy Eucharist from those Catholic politicians who publicly support abortion, the underlying assumption seems to be that the withholding of the sacrament from an unworthy recipient is no more than a matter of the minister's discretion, if such action is allowable at all. However, the teaching of the moralists was quite the opposite. Indeed, the moralists wrote with clarity on the duty of refusing the sacraments to the unworthy. In the twentieth century between 1917 and 1983, the commentary of moralists was often based upon Canon 855 of the 1917 (Pio-Benedictine) Code of Canon Law: “Those who are notoriously unworthy are to be refused, such as the excommunicated, the interdicted, and manifestly infamous, as are strumpets, those living in concubinage, usurers, wizards, sorcerers, blasphemers, and other public sinners of that kind, unless it is certain that they have repented and amended, and have made satisfaction for the public scandal which they have given.” From a moral point of view, administering the sacraments to those unworthy to receive represented, at least, material cooperation in another’s sin. In the case of public sinners, scandal imposes an additional moral problem.
Archbishop Raymond Burke has presented a very thorough explanation of the canonical aspects of the current text of the law found in canon 915 of the current Code of Canon Law. The article, "The Discipline Regarding the Denial of Holy Communion to Those Obstinately Perservering in Manifest Grave Sin," may be found in Periodica de Re Canonica, vol. 96 (2007): 3-58. (A copy of the article can be found at http://www.therealpresence.org/eucharst/holycom/denial.htm).