In those days the Church was not merely a thermometer that recorded the ideas and principles of popular opinion; it was a thermostat that transformed the mores of society.
Type of figurative language: it is a 'metaphor', which is a figure of speech that makes an implicit or hidden comparison between two unrelated things.
Meaning of figurative language: in this case, the metaphor is used to compare the Church with a thermometer or a thermostat that measures the humor in society.
Effect on tone and mood: As regards the tone, the author uses this metaphor to make it easy to understand the role of the Church. As regards the mood, the author conveys a serious atmosphere to the text.
Effect on the audience: It allows the audience to have a better idea of the social situation lived in those days.
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: It is also a metaphor.
Meaning of figurative language: In this case, the metaphor is used to explain the act of helping the Jewish people in terms of something forbidden, in terms of the law.
Effect on tone and mood: The author compares helping the Jewish with something illegal to show the seriousness of the social situation.
Effect on the audience: The audience is left with the feeling that nobody could help the Jewish.