Purifying oneself is of course not the only purpose for producing social justice. In fact, it generally never is the individual's purpose, it's only the consequence. Producing the result of justice has plenty of moral significance, because it moves other activities in a constructive direction and teaches by example what morality is. There are a lot of vagaries that need to be addressed in terms of what is justice and how to produce it. To clear up vagaries, definitions are absolutely essential.
Definitions can vary, but a good starting point is needed to show how all of the factors interact.
Justice is the result which truth produces. For example, if Congress passes a good bill, it's because the truth caught up to them, not because they happened to be moral that day. Only if the power of truth flows in that direction, can justice be produced. So truth needs to be understood. Truth is the ability to bring the universe down and apply it to human activities.