Answer:
It was "illegal" to aid and comfort a Jew in Hitler's Germany. But I am sure that, if I had lived in Germany during that time, I would have aided and comforted my Jewish brothers even though it was illegal.
Type of figurative language: Allusion
Meaning of figurative language: Dr. King believed in doing what's right, regardless of legality.
Effect on tone and mood: This gives a serious tone and mood to the letter.
Effect on audience: This makes the audience have empathy.