Whewell therefore starts with Justice in terms of the primary notion in light of which 'justice' and cognate words were understood in the eighteenth and nineteenth century, property. Yet simply focusing on property is not sufficient -- Benevolence, for instance, also may be concerned with property, as we see with Virtues like Charity and Liberality. The issue that seems to arise with property, insofar as Justice is concerned, is that property and wealth are means to ends, and thus use of them gets its value from the value of the ends; but one may also treat them as if they were merely ends in themselves. This is why greed is a negative term, for instance, and yet is contrasted with Virtues like Economy or Frugality. This also explains why Justice applies to things that do not deal with property as such -- property is a form of power, and the seeking of forms of power in general as if power were itself an end rather than a means to a further end is vicious Ambition, while seeking them for good further ends is laudable Ambition; the former is inconsistent with, and the latter an expression of, Justice even if no property is involved. When judging in personal matters, the Virtue expressing Justice is Fairness or Impartiality, the disposition that "represses our own desires, whether of money, power, victory, or any other object; and contemplates the desires and claims of other persons with equal favor" (EM §254).
Thus we get the Idea of Justice, which is that of "a Desire that, of external things, each person should have his own, without any preference of ourselves to others, or of one person to another" (EM §269). The Principle of Justice, expressing the object here, can be summarized as "Each Man is to have his own." When this principle is recognized to apply to desire itself, as it must to be a fully moral principle, we get its full force as a source of Duties (EM § 307):
The Duty of a Spirit of Justice excludes all Cupidity or eagerness in our desires of wealth; all Covetousness, or wish to possess what is another's; all Partiality, or disposition to deviate from equal Rule in judging between ourselves and others. The Rule of action is, Let each man have his own; but the Rule of desire is, Let no man seek his own, except so far as the former Rule directs him to do so. Justice gives to each man his own: but each ought to cling to his own, not from the love of riches, but from the love of Justice.
Because it applies to desires, there is in the case of Justice as in the case of Benevolence a duty of moral self-culture; we must develop the practice of seeking and holding property as something only to be done for Justice, and when we claim our just rights it should be as part of our effort to make sure that everyone can claim their just rights.
As with Benevolence, the effect of Christian morality on Justice is to intensify and incentivize. The opposition to cupidity of any kind, in fact, plays a major role in the moral precepts found throughout the New Testament. The early Christians were a small community within a much larger population, and so, Whewell notes, they had a tendency to emphasize their opposition to the vices of that larger society, among which were love of money and oppression of the poor. In the same way, and for the same reason, the moral precepts of the New Testament often indicate that Christians should avoid standing too much on their rights.
The Duties of Justice for states are much what one would expect, and are heavily concerned with matters of remedy for inequalities arising through history, in such a way as respects the rights of all involved.