C. To show that the General had a difficult time saying something.
Explanation:
In this excerpt, Twain uses the expression "to find his voice." This is an idiom that means that the general could not speak. This is Twain's way to say that the General had a difficult time saying something. This is likely a consequence of the fact that the General is in shock due to the actions of the man.
Providing background on the Renaissance would allow Charlie to talk about the shared history. This leads to talking about the effect the period had on art, and then specifically on the artists mentioned.
