In What Saint Paul Really Said, NT Wright does a great job supplying the meaning to a lot of Paul's language regarding justification, righteousness, justice, and other words in the dikai- word group...
"First, it is covenant language – not in the sense of that word made famous through some 16th and 17th century discussions, but in the 1st century Jewish sense. When Paul speaks of justification he is operating within the whole world of thought of second-temple Judaism, which clung to the covenantal promises in the face of increasingly difficult political circumstances.
Second, it is law-court language, functioning within the covenantal setting as a strong explanatory metaphor. Two thing must be said about this. First, this metaphor is necessary for understanding what the covenant was all about. The covenant was there to put the world to rights, to deal with evil and to restore God’s justice and order to the cosmos. Second, it is never independent of the covenant setting. It cannot be made in to an absolute and free-standing concept without doing violence both to itself and to the fundamental meaning of the covenant.
Third, justification for Paul cannot be understood properly apart from eschatology. It cannot, that is, be made into an abstract or timeless system, a method of salvation to be randomly applied. It is part of the Pauline worldview in which the creator of the world has acted, uniquely, climactically, and decisively, in Jesus Christ, for the rescue of the entire cosmos, and is now, by his Spirit, bringing all things into subjection to this Jesus."