In verse 20 Paul goes on to say, “Brothers, do not be children in your understanding, but in malice be babes, and in your understanding become full-grown.” The Corinthian believers were not only infants in life (3:1), but also children in understanding. They needed to grow both in life and in the understanding of their mind. All the apostle’s dealings with their problems were for this purpose, that they might mature in every way.
The Greek word translated understanding also means thinking, reasoning, mind. In Greek it is different from the word for mind in verses 15 and 19. It “emphasizes the distinction from ecstasy” (Vincent). This is in regard to the Corinthian believers’ understanding and thinking concerning speaking in tongues. They were ecstatic in this practice, thus childish in their understanding concerning it, not using their mind properly as a matured believer should. The apostle advises them to grow and become full-grown in their understanding, that is, in the proper use of their mind, as he uses his (v. 19), in the matter of tongue-speaking. The childish Corinthian believers needed to become full-grown in their understanding so that they might be able to know the things which are to be mentioned in verses 21 through 25.
Verse 21 says, “In the law it is written, In other tongues and with other lips I will speak to this people, even so they will not listen to Me, says the Lord.” The law in this verse refers to the Old Testament. This word in Isaiah 28:9-13 indicates that the speech in strange tongues was a chastisement for the children of Israel’s unbelief toward the intelligible word of God. Hence, the apostle’s quotation of this word implies that the Corinthians have not properly received the intelligible revelation of God through the apostles.
Verse 22 continues, “So then tongues are for a sign, not to those who believe, but to the unbelievers; but prophecy is not to the unbelievers, but to those who believe.” “So then” at the beginning of this verse indicates that according to the word in verse 21 quoted from Isaiah 28, tongues are for a negative sign to the unbelievers, signifying their poor condition of unbelieving. It implies that whenever or wherever a strange tongue is spoken, peoples’ unbelief is there. The apostle’s intention here is to hold the Corinthians back from their excessive practice of speaking in tongues. But prophecy is for a positive sign to those who believe, signifying their proper condition of believing. This is an encouragement to the practice of prophesying. The fact that tongues are a sign to unbelievers may indicate that those who want to receive the gift of tongues may have an evil heart of unbelief.
Verse 23 says, “If therefore the whole church comes together in one place, and all speak in tongues, and the unlearned or unbelievers enter, will they not say that you are insane?” Paul’s word about all speaking in tongues refers to all the functioning ones, not to all the attendants in the meeting. If in a meeting all the functioning ones speak in tongues, others may consider they are mad. Hence, to encourage all to speak in tongues in the church meeting is not right; it is against Paul’s word.
The Greek word rendered insane also means mad, raving mad. This word is a strong discouragement to the excessive practice of speaking in tongues.
In verse 24 Paul says, “But if all prophesy and some unbeliever or unlearned person enters, he is convicted by all, he is judged by all.” The phrase “all prophesy” refers to all the functioning ones, not to all the members of the church in the meeting. If all the functioning ones prophesy in the church meeting, this will convict others. This kind of prophesying must not be mainly to predict, but to speak for the Lord and speak forth the Lord.
The matter of being convicted by all, judged by all, must not be by the prophecy of prediction, but by the prophecy of speaking for the Lord and speaking forth the Lord. This kind of prophecy requires some amount of growth in life. This word is also an encouragement to the practice of prophesying.
In verse 25 Paul concludes, “The secrets of his heart become manifest; and so falling on his face, he will worship God, reporting that God is really among you.” This implies that prophecy, speaking for God and speaking forth God with God as its content, ministers God to the hearers and brings them to God. This also indicates that the church meeting should be filled with God, and all its activities should convey and transmit God to others so that they may be infused with God.