Section — Slater, Manual of Moral Theology
Section III. The Duty of Administering the Sacraments
All who have the cure of souls are bound in justice and in charity to administer the sacraments to the members of their flock when these need them or ask for them reasonably. The obligation is principally one of justice, and it arises from the implicit contract which those who have the cure of souls enter into on assumption of office. The obligation is a grave one if the subject is in extreme or grave necessity, and even when there is no grave necessity one who has the cure of souls would commit serious sin if he frequently refused the sacraments to those who ask for them reasonably. An occasional refusal in such cases would not be a grievous sin, as although the spiritual good of which they are unjustly deprived is considerable, yet the loss can without much inconvenience be made good at another time.
The obligation of justice is so strict that those who have the cure of souls are bound even at the risk of life to administer the sacraments to their flock in extreme or in grave necessity. This obligation, however, only extends to those sacraments which are necessary for salvation, such as Baptism and Penance; it does not extend to those which are not necessary, not even to the holy Eucharist, according to a very probable opinion. Mortal sin will be committed not only by frequent refusal of the sacraments to those who ask for them in a reasonable manner, but also by making one’s self difficult to approach and by an ungracious manner of yielding to reasonable requests, inasmuch as such methods deter the faithful from exercising their just rights.
p. ii, 66–67
Ministers of the sacraments who have not the cure of souls are bound in charity to administer the sacraments to such as are in extreme or grave spiritual necessity. This obligation is less strict than that which lies on those who have the cure of souls, so that those who have no such cure will only be bound at the risk of life to administer the sacraments which are necessary for salvation to those who are in extreme necessity. But in order that this grave obligation of charity may exist there must be moral certainty that the person in question is in extreme spiritual necessity, or in other words, that he is in proximate danger of damnation unless the sacraments be administered. There must also be a reasonable certainty that the attempt to administer the sacraments will be successful; it would be hard if a minister of the sacraments were bound to imperil his life for a mere probability of being able to help another in spiritual distress. Furthermore, before so grave an obligation can be imposed on anyone it must be morally certain that he who is in spiritual necessity is unable to help himself by making an act of contrition for his sins or of perfect love of God, and that there is no one else who is able and willing to succour him in his necessity. As all these conditions are seldom verified in any concrete case, it is apparent that those who have not the cure of souls will seldom be under a grave obligation of administering the sacraments to those who are in extreme necessity at the risk of life.
p. ii, 67