This same petition proves that the doctrine of justification is the kind of thing that can never be learned completely. Therefore it is true that those who have persuaded themselves that they know it fully have not even begun to learn.
Because every day new struggles arise from Satan and our flesh or the world or our conscience, prompting us to despair, wrath, lust, and other vices, how is it possible for this weakness of ours not to keep falling or breaking? Then, too, how many concerns arise in this life that gradually make us forget this gladness? Hence it is supremely necessary that we ask God to pour or sprinkle upon us this hearing of joy so that we are not covered with the sadness that the feeling of sin brings on.”