16. Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me. For if l pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. Else when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest? For thou verily givest thanks well, but the other is not edified (I Corinthians, 14: 11, 14, 16 & 17).
17. The value of prayer comes from the thought to which it is united. So it is impossible to join any thought to something that is not understood, since what is not understood cannot touch the heart. For the great majority of human beings prayers that are said in an unknown language are nothing more than a conglomeration of words which say nothing to the Spirit. In order for prayer to touch one, it is necessary for each word to awaken an idea, and when the words are not comprehended they are unable to do this. It would be merely a simple formula, whose virtue depended on the greater or lesser number of times it was repeated. Many pray from duty, others from obedience to habit; this is why they judge themselves to be exonerated from their duty after having prayed a determined prayer a sufficient number of times, in a certain order. God reads what passes deep in our hearts. He scrutinizes our thought and our sincerity; therefore in judging Him to be more sensitive to the format rather than the depth is to discredit Him (See chapter 28, item 2).