A friend sent this my way, evidently posted by a priest on Facebook:
“A friend and parishioner went to another parish last weekend. Evidently, a deacon candidate was preaching, which is problem number one. Yes, I know. Practice, blah, blah, blah. But only clerics can preach at Mass. But, Father, it was a ‘reflection’. Listen, if it sounds like a homily and is in the place of a homily, it is a homily. However, the bigger problem was that he said that he and his wife were going to be deacons. NO! Deacons’ wives have no additional status. There is NOT now, never has been, and will never be ‘deacon couples’. This needs to be topic one in diaconal formation and made crystal clear to the wife of a potential deacon.”
Well, the priest pretty much summed it up. But if anyone has any doubts:
1. Deacons are ordained. Their wives are not. Priests are ordained. Their wives are not. Period.
2. As a result, there really isn’t such a thing as a “deacon couple.” Just as there is no such thing as a “priest couple.” On a hunch, pondering other faith traditions, I suspect there is no such thing as a “rabbi couple” or a “minister couple,” either.
3. Deacon candidates really should not be preaching at Mass in the place of a homily. (Seminarians who are not yet ordained deacons shouldn’t be doing it, either.) If a pastor thinks a candidate needs the practice, there are other avenues available; he can offer a reflection during Benediction, at Evening or Morning Prayer, at a Baptism, at a Liturgy of the Word prayer service or at a wake. (I imagine, under some circumstances, he might even be invited by the priest or deacon to offer a few words during a simple exchange of vows at a wedding.) But during Mass? No.
Regarding who may preach at Mass: there’s an excellent summary from a few years ago over at the blog Canon Law Made Easy. Check it out. There are explicit references to the Code of Canon Law, and a distinction is clearly made between a “homily” and a “sermon,” and between speaking at Mass and in other settings.