78 The morality of the human act depends primarily and fundamentally on the "object" rationally chosen by the deliberate will, as is borne out by the insightful analysis, still valid today, made by Saint Thomas. In order to be able to grasp the object of an act which specifies that act morally, it is therefore necessary to place oneself in the perspective of the acting person. The object of the act of willing is in fact a freely chosen kind of behaviour. To the extent that it is in conformity with the order of reason, it is the cause of the goodness of the will; it perfects us morally, and disposes us to recognize our ultimate end in the perfect good, primordial love. By the object of a given moral act, then, one cannot mean a process or an event of the merely physical order, to be assessed on the basis of its ability to bring about a given state of affairs in the outside world. Rather, that object is the proximate end of a deliberate decision which determines the act of willing on the part of the acting person. Consequently, as the Catechism of the Catholic Church teaches, "there are certain specific kinds of behaviour that are always wrong to choose, because choosing them involves a disorder of the will, that is, a moral evil". And Saint Thomas observes that "it often happens that man acts with a good intention, but without spiritual gain, because he lacks a good will. Let us say that someone robs in order to feed the poor: in this case, even though the intention is good, the uprightness of the will is lacking. Consequently, no evil done with a good intention can be excused. 'There are those who say: And why not do evil that good may come? Their condemnation is just' ( Rom 3:8)". The reason why a good intention is not itself sufficient, but a correct choice of actions is also needed, is that the human act depends on its object, whether that object is capable or not of being ordered to God, to the One who "alone is good", and thus brings about the perfection of the person. An act is therefore good if its object is in conformity with the good of the person with respect for the goods morally relevant for him. Christian ethics, which pays particular attention to the moral object, does not refuse to consider the inner "teleology" of acting, inasmuch as it is directed to promoting the true good of the person; but it recognizes that it is really pursued only when the essential elements of human nature are respected. The human act, good according to its object, is also capable of being ordered to its ultimate end. That same act then attains its ultimate and decisive perfection when the will actually does order it to God through charity. As the Patron of moral theologians and confessors teaches: "It is not enough to do good works; they need to be done well. For our works to be good and perfect, they must be done for the sole purpose of pleasing God".
Source: Veritatis Splendor (Vatican.va)