US-P18.010ab ।US-P18.010cd ॥
In plain words
There are listeners who know exactly what the sentence means and still do not take it in when it is spoken once. For that reason alone, such a person needs something further — and we have already said what it is, for it comes as a pair.
Close to the Sanskrit
He who, even being a knower of the sentence's meaning, would not grasp what has been said once — for just that reason he requires something else; we have spoken of it, for that is twofold.