This is a phrase that I would not consider unusual at all. It is synonymous for telling somebody off, as in really giving it to them with both barrels. It does not mean that swear words were not used. Perhaps there is an element of irony in its origin (and they say we Southerners don't have irony), although it is not used nowadays as a means of humor.

A similar phrase comes to mind: a word of prayer, as in, "Could you come over here a second? You and I need to have a word of prayer together." If someone says this to you, you're about to get a firm scolding. The difference is that when you bless somebody out, you're losing your cool, and when you take someone aside for a "word of prayer," it's more of a dish served cold, if you know what I mean.