Preaching rules can be broken but David Alan Black has a concise but good caution here about using (or misusing) Greek (or Hebrew for that matter) in preaching. I would disagree somewhat with the point that people are wholly uninterested in references to the original languages. I have found that they often are. The problem is that they are typically interested for the wrong reasons (e.g., it makes the preacher or preaching more authoritative, it settles complex interpretive problems, it makes a particular explanation of the text deeper, etc.). These misplaced notions are one reason why preachers are tempted to use the languages and a good reason why they should avoid doing so.
HT: Henry Neufeld