Justice
The original Hebrew and Greek words are the same as those rendered "righteousness." This is the common rendering, and in about half the cases where we have "just" and "justice" in the King James Version, the American Standard Revised Version has changed to "righteous" and "righteousness." It must be constantly borne in mind that the two ideas are essentially the same.
Human Justice
The word "justice" does not occur in the New Testament, and in most cases where we find "just" in the King James Version it is changed to "righteous" in the American Standard Revised Version. The idea of justice or righteousness (remembering that these are essentially the same) becomes more spiritual and ethical in the New Testament. It is a matter of character, and God’s own spirit is the standard (1 Joh 3:7; Mt 5:48). The mere give-and-take justice is not enough. We are to be merciful, and that to all. The ideal is righteousness, not rights. As Holtzmann says, "The keynote of the Sermon on the Mount is justitia and not jus."
Justice of God
God’s justice, or righteousness, is founded in His essential nature. But, just as with man, it is not something abstract, but is seen in His relation to the world. It is His kingship establishing and maintaining the right. It appears as retributive justice, "that reaction of His holy will, as grounded in His eternal being, against evil wherever found." He cannot be indifferent to good and evil (Hab 1:13). The great prophets, Isaiah, Micah, Amos, Hosea, all insist upon Yahweh’s demand for righteousness.
And God’s justice is not merely gracious, but redemptive. It not simply apportions rights, it establishes righteousness. Thus, just as in the Old Testament, the judge is the Saviour. The difference is simply here: in the Old Testament the salvation was more national and temporal, here it is personal and spiritual. But mercy is opposed to justice no more here than in the Old Testament. It is by the forgiveness of sins that God establishes righteousness, and this is the supreme task of justice. Thus it is that God is at the same time "just, and the justifier of him that hath faith in Jesus" (Ro 3:26). "He is faithful and righteous (or "just"; see the King James Version) to forgive us our sins, and to cleanse us from all unrighteousness" (1 Joh 1:9).
Bibliography
Comm., and Biblical Theologies under "Justice" and "Righteousness," and especially Cremer, Biblical-Theol. Lex. of New Testament Greek