Question

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?
to appeal to his critics’ sense of duty
to describe an historical precedent
to commemorate a famous leader
to encourage a consideration of ethics

Answer 1

to encourage a consideration of ethics

He invokes Aquinas’s natural-law argument to frame laws in moral terms—showing that laws must be judged by higher ethical standards, not just legal authority.