Saint Thomas Aquinas taught that the Church’s moral teaching has its own “hierarchy”, in the virtues and in the acts which proceed from them.39 What counts above all else is “faith working through love” (Gal 5:6). Works of love directed to one’s neighbour are the most perfect external manifestation of the interior grace of the Spirit: “The foundation of the New Law is in the grace of the Holy Spirit, who is manifested in the faith which works through love”.40 Thomas thus explains that, as far as external works are concerned, mercy is the greatest of all the virtues: “In itself mercy is the greatest of the virtues, since all the others revolve around it and, more than this, it makes up for their deficiencies. This is particular to the superior virtue, and as such it is proper to God to have mercy, through which his omnipotence is manifested to the greatest degree”.41
38 Second Vatiati can Ecumenical Council, Decree on Ecumenism Unitatis Redintegratio, 11.
39 Cf. S. Th., I-II, q. 66, a. 4-6.
40 S. Th., I-II, q. 108, a. 1.
41 S. Th., II-II, q. 30, a. 4: “We do not worship God with sacrifices and exterior gifts for him, but rather for us and for our neighbour. He has no need of our sacrifices, but he does ask that these be offered by us as devotion and for the benefit of our neighbour. For him, mercy, which overcomes the defects of our devotion and sacrifice, is the sacrifice which is most pleasing, because it is mercy which above all seeks the good of one’s neighbour” (S. Th., II-II, q. 30, a. 4, ad 1).