Tenses in summarizing a story
I came across the following explanation in 'The Elements of Style':
In summarizing the action of a drama, use the present tense. In summarizing a poem, story, or novel, also use the present, though you may use the past if it seems more natural to do so.... But whichever tense is used in the summary, a past tense in indirect discourse or in indirect question remains unchanged.
The Friar confesses that it was he who married them. (Example given in the book)
Could anyone explain
1. when is it 'seems more natural' to use the past form of verbs when summarizing a story?
2. what does the last sentence of the paragraph mean?