Please explain, "My warbling lute . . . / . . . The lute and sword which he in triumph bore . . ." from John Dryden's "My Last Duchess."
Actually, the line you quote here isn't from "My Last Duchess," but is instead from MacFlecknoe. Both, of course, are by John Dryden. My guess is that you were looking at a list of Dryden's poems and chose the second alphabetical one by mistake. Regardless, let's take the final lines of the quote in order to answer to your question:
Pale with envy, Singleton forswore
The lute and sword, which he in triumph bore,
And vowed he ne’er would act Villerius more.
—Dryden: MacFlecknoe (1682).
This is a definite reference to Davenant’s Siege of Rhodes(1656) known as the first English opera and based on the true Seige of Rhodes in 1522. Villerius or, I'm guessing, "Villiers de L'Isle-Adam" defended Rhodes against many attacks only to submit to a truce after being bombarded by Turks again and again. Villerius, then, is the grand hero (or failure) of this great siege, and would therefore be the main character of the opera. When Singleton gives up his lute and sword that he used to wield in triumph, he vows never to play that part again because there is someone much better to play that part: Shadwell who "All arguments, but most his plays, persuade, That for anointed dullness he was made." So continues Dryden's mock-heroic poem praising the anointed monarch of dullness.