Final answer:
Lines 13-16 contribute to the development of the poem's theme by emphasizing the subjective nature of beauty.
Step-by-step explanation:
Lines 13-16 contribute to the development of the poem's theme by emphasizing the idea of beauty being subjective. In these lines, the speaker mentions how ribbons in the first stanza and flames in the second stanza are seen as beautiful by the speaker and believers, despite their harmful nature. This suggests that beauty is not objective, but rather depends on individual perception.