Albert Barnes Commentary 1 Corinthians 14:22

"Wherefore tongues are for a sign, not to them that believe, but to the unbelieving: but prophesying [is for a sign], not to the unbelieving, but to them that believe." — 1 Corinthians 14:22 (ASV)

Wherefore. Thus, (Greek: hōste), or therefore. The apostle does not mean to say that what he was about to state was a direct conclusion from the passage of Scripture he had quoted, but that it followed from all 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, evidence, or proof that God has imparted this power and that He accompanies the preaching of the gospel with His approval. 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 would not be benefited by what was spoken in a language 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 speaking in this way; and since it was conferred expressly to aid in the propagation of the gospel, it proved that it was from God. (See Barnes' notes 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 Barnes' notes on 1 Corinthians 14:1).

For them that believe not. Prophesying is not particularly intended for them but is mainly for edifying the church. It is not as striking, nor as filled with proofs of the divine presence and power, as the gift of tongues. Though it may truly be under the influence of the Holy Spirit and genuinely by inspiration, it is not as evidently so as the power of speaking foreign languages.

Therefore, it was better suited to edify the church than to convince opponents. At the same time, the truths it conveyed and the consolations it administered could be as clear evidence to the church of God's accompanying power, presence, and goodness, as the power of speaking foreign languages might be to unbelievers.