Not just any vocalist could pull off this embellishment and have it sound natural. At one point in "Oh, Come, All Ye Faithful," Lou Rawls sings, "Oh, come on, all ye faithful." That one added word, the way Rawls sings it, adds fervency to the carol's request that people gather and worship the Christ child. Except for Ray Charles, I can't imagine any other artist phrasing the request that way without sounding awkward.
