How We are to Decide Whom to Aid
29 Further, all men are to be loved equally. But since you cannot do good to all, you are to pay special regard to those who, by the accidents of time, or place, or circumstance, are brought into closer connection with you. For, suppose that you had a great deal of some commodity, and felt bound to give it away to somebody who had none, and that it could not be given to more than one person; if two persons presented themselves, neither of whom had either from need or relationship a greater claim upon you than the other, you could do nothing fairer than choose by lot to which you would give what could not be given to both. Just so among men: since you cannot consult for the good of them all, you must take the matter as decided for you by a sort of lot, according as each man happens for the time being to be more closely connected with you.
Source: Christian Doctrine (New Advent)