Which theme from Macbeth do these lines support? This supernatural soliciting
Cannot be ill, cannot be good. If ill,
Why hath it given me earnest of success,
Commencing in a truth?

Phrases such as “while I lived” and “the grace, the beauty, the poetry” indicate most about the narrator’s feelings  that Twain was disappointed by his new feelings about the river.

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