Learn English – How should I understand “tone” in this context

The following is a GRE sample question.

Jean Wagner’s most enduring contribution to the study of Afro-American poetry is his insistence that it be analyzed in a religious, as well as secular, frame of reference. The appropriateness of such an approach may seem self-evident for a tradition commencing with spirituals and owing its early forms, rhythms, vocabulary, and evangelical fervor to Wesleyan hymnals. But before Wagner a secular outlook that analyzed Black poetry solely within the context of political and social protest was dominant in the field.

It is Wagner who first demonstrated the essential fusion of racial and religious feeling in Afro-American poetry. The two, he argued, form a symbiotic union in which religious feelings are often applied to racial issues and racial problems are often projected onto a metaphysical plane. Wagner found this most eloquently illustrated in the Black spiritual, where the desire for freedom in this world and the hope for salvation in the next are inextricably intertwined.

All of the following aspects of Afro-American poetry are referred to in the passage as having been influenced by Wesleyan hymnals EXCEPT:
(A) subject matter
(B) word choice
(C) rhythm
(D) structure
(E) tone

I'm quite sure that the answer should be based on the sentence in bold:

The appropriateness of such an approach may seem self-evident for a tradition commencing with spirituals and owing its early forms, rhythms, vocabulary, and evangelical fervor to Wesleyan hymnals.

And by the words "forms", "rhythms", and "vocabulary", I think one can rule out D, C, and B. The conundrum is between A and E. I'm not able to determine which one is more related to "evangelical fervor". I looked the words "subject matter" and "tone" in the dictionary and I found that the subject matter of something such as a book, lecture, film, or painting is the thing that is being written about, discussed, or shown, and that the tone of a speech or piece of writing is its style and the opinions or ideas expressed in it. Neither one, as I understand so far, is related to "evangelical fervor". How should I understand "tone" in this context? Does it have anything to do with "evangelical fervor"?