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. Why does king use this allusion

King was a minister criticized by clergymen, so he tried to justify his cause by paraphrasing the words of Thomas Aquinas, a notable interpreter of God's order on earth. He uses this allusion because he wants to underline the crucial difference between just and unjust law, that has been confirmed by one of the highest intellectual authorities in the fields of philosophy and religion. King provides a religious justification for the concept of nonviolent resistance.