—That is—you'll not mistake an idle word Spoke in a huff by a poor monk, God wot, Tasting the air this spicy night which turns The unaccustomed head like Chianti wine! Oh, the church knows! don't misreport me, now! It's natural a poor monk out of bounds Should have his apt word to excuse himself: And hearken how I plot to make amends.
Lippo seems to notice that maybe he's spoken too hastily about the higher-ups at the monastery, since he cautions the guardsman to not dwell too much on his "idle word[s]." After all, he is drunk (on a good Chianti... hopefully sans human liver and fava beans). He's not used to drinking much so his slip of the tongue should be forgiven. (Yeah, right—we believe you Lippo.)
He hopes the guard won't report his disobedient words to the Church, because it's really natural that Lippo would speak this way, since he's so out of his element.
He seems to be quite the smooth talker, our Lippo.
Now, he's going to tell the guardsman how he'll make things right with the Church.