That title may strike you as a bit odd--didn't you just thank Them a minute ago?

Well, yes, but there's more to it than that. What you are doing here is thanking the Lord and Lady for Their presence and telling them that the ritual is over. It's pretty much the opposite of invoking them (although I'm certainly not going to tell Them that They must leave--if They want to hang around, it's fine by me).

An example of this might be: "Lord and Lady, I thank you for attending this rite, which is now done. So mote it be."