D(set in motion, cause to start
I would agree with you - the conclusion should leave readers with an important thought at the end.
This thought should never be new, or opposing to the previous ideas you had been writing before. It also shouldn't be confusing, but quite conversely - it should explain everything and put everything in place.
Phrases such as “while I lived” and “the grace, the beauty, the poetry” indicate most about the narrator’s feelings <em>that Twain was disappointed by his new feelings about the river.
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When he says “While I lived” He referrers to the time he had spent in the river, the adventures, the excitement.
The grace, the poetry, the beauty describes the way the narrator has always seen the river, as a magnificent scenario full of life and susprises. A place where he has lived his most amazing adventures
