The title borrows the old saying that the pen is mightier than the sword, and the poem turns it into something stranger and more literal. The speaker kills a colonel with a pen, as if writing could be a weapon in the plainest sense. There is no "treaty to commend him," so no paper peace and no official ceremony. The colonel is simply gone, and the speaker notes, almost with satisfaction, "How quiet he is!"
The second half moves from violence to appetite. The speaker "dines on a great oar," pays a servant to do the rowing, and rests. The images are odd and dreamlike, so it's hard to say exactly what happens. Still, the tone is clear enough: cool, dry, a little smug. The speaker seems at ease, even lazy, after the deed. The mood is darkly playful, and it hints that words can silence authority while someone else does the labor of carrying on.