Therefore tongues are for a sign This passage may be explained in two ways, by considering the word therefore as referring merely to the preceding sentence, or as having a bearing generally on the whole of the foregoing discussion. If it is a particular inference, the meaning will be -- "You see, brethren, that what you so eagerly desire is not a blessing bestowed by God upon believers, but a punishment, by which he inflicts vengeance upon unbelievers." In this way, Paul would not be viewed as taking in the use of tongues under all circumstances, but simply as touching upon what had in one instance occurred. Should any one, however, prefer to extend it to the whole discussion, I have no objection, though I do not dislike the former interpretation. Taking it in a general way, the meaning will be "Tongues, in so far as they are given for a sign -- that is, for a miracle -- are appointed not properly for believers, but for unbelievers." The advantages derived from tongues were various. They provided against necessity -- that diversity of tongues might not prevent the Apostles from disseminating the gospel over the whole world: there was, consequently, no nation with which they could not hold fellowship. They served also to move or terrify unbelievers by the sight of a miracle -- for the design of this miracle, equally with others, was to prepare those who were as yet at a distance from Christ for rendering obedience to him. Believers, who had already devoted themselves to his doctrine, did not stand so much in need of such preparation. Hence, the Corinthians brought forward that gift improperly and out of its right place, allowing prophecy in the meantime to be neglected, which was peculiarly and specially set apart for believers, and ought, therefore, to be familiar to them, for in tongues they looked to nothing farther than the miracle.

Wherefore - Thus, (Ὥστε Hōste), or wherefore. The apostle does not mean to say that what he was about to state was a direct conclusion from the passage of Scripture which he had quoted, but that it followed from all that he had said, and from the whole view of the subject. "The true statement or doctrine is, that tongues are for a sign," etc.
Tongues - The power of speaking foreign languages.
Are for a sign - An "indication," an evidence, or a proof that God has imparted this power, and that he attends the preaching of the gospel with his approbation. It is a "sign," or a "miracle," which, like all other miracles, may be designed to convince the unbelieving world that the religion is from God.
Not to them that believe - Not to Christians. They are already convinced of the truth of religion, and they would not be benefited by that which was spoken in a language which they could not understand,
But to them that believe not - It is a miracle designed to convince them of the truth of the Christian religion. God alone could confer the power of thus speaking; and as it was conferred expressly to aid in the propagation of the gospel, it proved that it was from God; see the note on Acts 2:1-15.
But prophesying - Speaking in a calm, connected, didactic manner, in language intelligible to all under the influence of inspiration; see notes on 1-Corinthians 14:1.
For them that believe not - Is not particularly intended for them; but is intended mainly for the edifying of the church. It is not so striking, so replete with proofs of the divine presence and power as the gift of tongues. Though it may be really under the influence of the Holy Spirit, and may be really by inspiration, yet it is not so evidently such as is the power of speaking foreign languages. It was, therefore, better adapted to edify the church than to convince gainsayers. At the same time the "truths" conveyed by it, and the consolations administered by it, might be as clear evidence to the church of the attending power, and presence, and goodness of God, as the power of speaking foreign languages might be to infidels.

Wherefore tongues are for a sign - The miraculous gift of tongues was never designed for the benefit of those who have already believed, but for the instruction of unbelievers, that they might see from such a miracle that this is the work of God; and so embrace the Gospel. But as, in the times of the prophet, the strange Babylonish tongues came in the way of punishment, and not in the way of mercy; take heed that it be not the case now: that, by dwelling on the gift, ye forget the Giver; and what was designed for you as a blessing, may prove to you to be a curse. For if, because ye have the gift of tongues, ye will choose for your own aggrandizement to use them in the public congregation where none understands them, God may curse your blessings.
Prophesying - Teaching the things of God in a known language is of infinitely more consequence than speaking in all the foreign tongues in the universe.

(10) Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying [serveth] not for them that believe not, but for them which believe.
(10) The conclusion: therefore the gift of tongues serves to punish the unfaithful and unbelievers, unless it is referred to prophecy (that is to say, to the interpretation of scripture) and that what is spoken is by the means of prophecy is understood by the hearers.

Wherefore tongues are for a sign,.... Of wrath and punishment inflicted on a rebellious and unbelieving people, and not of grace and kindness, as prophesying, or speaking to them by the prophets, was; and so this is an inference from what is said in the preceding verse, and shows, that there was no reason why believers should be so very desirous of them. But if these words refer to all that is said before on this subject, the word "sign" may be taken for a miracle; and so a new argument is formed against an over fondness for divers tongues, and the use of them in public worship, showing the preferableness of prophecy to them; for speaking with divers tongues was used in a miraculous way,
not to them that believe; who have no need of miracles to raise their attention to what is said, and that it may gain credit with them, or to confirm their faith in it:
but to them that believe not; to prepare them to listen to what might be suggested to them, when they see the persons speaking were endued with miraculous powers, and to engage their assent to it, and belief of it; and so with such persons, and for such purposes, was the gift of speaking with divers tongues used by the apostles, Acts 2:4 but inasmuch as the Corinthian church consisted of believers, there was no need of such a sign or miracle among them; wherefore, if they desired such gifts, and to make use of them, they should choose to do it, not in the church, but among unbelievers:
but prophesying serveth not for them that believe not; that is, not for them only; for prophesying or explaining the prophetic writings, or preaching the word, may be, and often is, the means of converting unbelievers; yet this is not the only use, nor does it serve for, or administer comfort to unbelievers as such; but is profitable to, and serves
for them which believe: it is for their edification, exhortation, and comfort, 1-Corinthians 14:4 it is the means of building them up on their most holy faith; of quickening and stirring them up to the exercise of grace, and performance of duty; of comforting them under various distresses, inward and outward; and of establishing, strengthening, and settling them, and therefore much more eligible to be used in a church of Christ, than speaking with tongues.

Thus from Isaiah it appears, reasons Paul, that "tongues" (unknown and uninterpreted) are not a sign mainly intended for believers (though at the conversion of Cornelius and the Gentiles with him, tongues were vouchsafed to him and them to confirm their faith), but mainly to be a condemnation to those, the majority, who, like Israel in Isaiah's day, reject the sign and the accompanying message. Compare "yet . . . will they not hear Me" (1-Corinthians 14:21). "Sign" is often used for a condemnatory sign (Ezekiel 4:3-4; Matthew 12:39-42). Since they will not understand, they shall not understand.
prophesying . . . not for them that believe not, but . . . believe--that is, prophesying has no effect on them that are radically and obstinately like Israel (Isaiah 28:11-12), unbelievers, but on them that are either in receptivity or in fact believers; it makes believers of those not wilfully unbelievers (1-Corinthians 14:24-25; Romans 10:17), and spiritually nourishes those that already believe.

Tongues are intended for a sign to unbelievers - To engage their attention, and convince them the message is of God. Whereas prophecy is not so much for unbelievers, as for the confirmation of them that already believe.