“We dismiss what philosophers take to be the fundamental exercise of justice,” writes Ambrose in his Christianized Ciceronian treatise de officiis (translation, From Irenaeus to Grotius, 84-5). According to Ambrose's summary, philosophical justice takes as “the primary criterion . . . that we do no harm except in return for harm done,” a principle rejected by Jesus.
The second philosophic principle is “to treat common or public property as public, private as private.” Ambrose considers this distinction unnatural: “Nature's bounty is universal, for the common use of all. God has so ordained the law of universal generation that there is common food for all and that the earth is a kind of common possession.” Common right is rooted in nature, while greed is the source of private right.
Citing Stoic doctrine, Ambrose says that “the earth was created for the use of men, but . . . men came forth for men's sake, to be of help to one another.” Thus it's God's will that we are “of help to one another and . . . vie with each other in rendering services; we ought to put all our advantages in the common pool, as it were, and be a ‘helper' (as Scripture says) by sympathetic interest, by discharging responsibilities, by giving money, by performing tasks, or however.” In this way, “the attractiveness of human fellowship may be seen among us to the best advantage.” This is Christian justice.
Justice defined in this way is “a resplendent quality.” Justice—“serving the good of others rather than the self”—is the condition for the possibility of “community and association”: “It holds the highest place, has everything subject to its judgment, offers help, supplies resources, does not refuse responsibility but accepts the risks that others bring.” Justice is “a veritable fortress of virtue, which any strategist would be glad to hold.”