He points out the way in which this gift can be made useful to many. He says, "He who speaks with tongues, let him be filled, that he may also receive the gift of interpretation." This means that they themselves are guilty of not receiving the gift of interpretation, because they do not ask God for it.

For when I pray in an unknown tongue, then although my spirit prays, my mind remains unfruitful.

In ancient times, some received the gift of prayer along with the gift of tongues, and pronounced Persian or Roman words, but the mind did not understand what they were saying. Paul also says that my spirit, that is, the gift that moves the tongue, prays, but my mind remains unfruitful, because it does not understand anything that is spoken. See, then, how he gradually proved that he who speaks only with the tongue is useless to himself. This is how St. John explains this passage. And some understand it thus: if I speak with the tongue and do not explain, then my spirit, that is, my soul, receives benefit of itself, but my mind remains unfruitful, because it does not benefit others. Those who thus understand this saying, in my opinion, feared the error of Montanus: for he introduced such a heresy that the prophets decidedly did not understand their speeches, but those who were possessed by the Spirit said something, and what they said they did not understand. But this is inappropriate here. For the apostle said this, that is, that they do not understand their words, not about the prophets, but about those who speak with tongues, and of them not all, but some.

What to do? I will pray in spirit, and I will pray in mind; I will sing with my spirit, I will sing with my mind.

What, he says, is more useful? and what should we ask of God? in order to pray in the spirit, that is, in the gift, and also in the mind, that is, in thought, to be aware of the words of the prayer. The same is true of singing.

For if you bless in the Spirit, how will he who stands in the place of the commoner say, "Amen" at your thanksgiving? For he does not understand what you are saying.

When, he says, you sing, if you bless with the spirit, that is, with spiritual gifts through the tongue, then the one who takes the place of the simpleton, that is, the layman, how will he say "Amen" during your prayer? For thou hast spoken the words "unto the ages of ages" vaguely, and in a tongue unknown to him, and he has not understood it, and therefore profiteth not.

You give thanks well, but the other is not edified.

Lest it be thought that the gift of tongues is decisively degrading, he says: "For your part, you give thanks well, but since there is no benefit to your neighbor, your thanksgiving is useless."

I thank my God, for I speak with tongues more than all of you.

Lest they think that he degrades this gift because he himself does not have it, he says: I speak with tongues more than anyone else.

But in church I would rather speak five words with my mind, in order to instruct others, than a thousand words in an unknown tongue.

By my mind, that is, by understanding and being aware of my own words, and being able to explain them in order to benefit others as well. Than a thousand words in an unknown tongue, that is, when I cannot interpret them; for in that case the benefit is limited to me alone. Five words are spoken by every teacher who applies a suitable medicine to each of our five senses.

Fraternity! Do not be children in mind: be infants in evil, but be of full age in mind.