Zeal

(From delos, a derivative of deo "to boil", to "throb with heat"), is "a necessary effect of love", being "the vehement movement of one who loves to [secure] the object of his love" (vehemens motus amantis in rem amatam, St. Thomas, Summa Theol. I-II:28:4). Here the distinctive note is in the vehemence, or intensity, of the action to which love impels, an intensity which is proportioned to that of the love felt. As there is two kinds of love, the amor concupiscentiae, which is self-regarding, and the amor amicitiae, which is altruistic, two corresponding kinds of zeal might be distinguished, but by usage the term is restricted to the zeal prompted by the amor amicitiae; indeed in its religious sense it is applied solely to the zeal inspired by the love of God, to the ardent endeavours and works undertaken to promote His glory. Here again we can subdivide according as this zeal for God manifests itself in works of devotedness directed towards the fulfillment of the first or the second of the two great Commandments. In the Bible (cf. Psalm lxiii, 10; Num., xxv, 11; Tit., ii, 14, etc.) it is mostly used in the first of these applications; in the phrase "zeal for souls" it is used in the second, and in this sense it is much the more common among religious writers.