Now, what is the difference between the two? How does one determine whether a law is just or unjust? A just law is a man made code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law. Any law that uplifts human personality is just. Any law that degrades human personality is unjust. All segregation statutes are unjust because segregation distorts the soul and damages the personality. It gives the segregator a false sense of superiority and the segregated a false sense of inferiority. Segregation, to use the terminology of the Jewish philosopher Martin Buber, substitutes an "I it" relationship for an "I thou" relationship and ends up relegating persons to the status of things. Hence segregation is not only politically, economically and sociologically unsound, it is morally wrong and sinful. Paul Tillich has said that sin is separation. Is not segregation an existential expression of man's tragic separation, his awful estrangement, his terrible sinfulness? Thus it is that I can urge men to obey the 1954 decision of the Supreme Court, for it is morally right; and I can urge them to disobey segregation ordinances, for they are morally wrong.
To read 'Letter from Birmingham Jail' is to be able to see and study King's mental processes close up. The 'Letter' was not accepted for publication in the paper that had printed the criticisms ('A Call for Unity') to which it responds. King's letter was not even widely distributed until years after the Birmingham protests. But it is now and has long been an opportunity for readers around the world to continue experiencing and learning from the moving, dynamic and undeniably reasonable rhetorical artistry of this legendary figure. Dr. King's letter was not the first or only important document in the history of modern civil rights, but it is now considered to be the central intellectual landmark in a major turning point of that movement.