Why does Dr. King compare just and unjust laws?

Though the “Letter from Birmingham Jail” is implicitly concerned with justice throughout, Dr. King also addresses the question directly at several points. In effect, he posits that justice upholds the dignity of the human spirit, while injustice works against it. By discussing this concept in general, philosophical terms, he establishes criteria by which to equivocally attack both segregation and silence in the face of it. In terms of this latter attack, he ultimately suggests that the man who sees injustice and does nothing to stop it is acting unjustly as well. Following this idea, he argues that laws must be imbued with a moral sense in order to be just; in other words, law and morality cannot be seen as separate pursuits or areas. It is significant that Dr. King frames his argument in terms of these universal values – rather than the simple political question of the day – since it makes the argument both more timeless and more unimpeachable.