Therefore tongues are for a sign, not to those who believe but to unbelievers; but prophesying is not for unbelievers but for those who believe.
The “therefore” introduces a purpose clause, giving the purpose of tongues. The “therefore” infers that the quotation from Isaiah 28 applies to the situation at Corinth. The “therefore” also gives a legitimate deduction from the Scripture just quoted in the previous verse. The purpose of tongues was as a “sign” to unbelieving Jews. There were many Jews in Corinth at the founding of the church (Acts 18:1-17).
This verse is the only specific statement of the purpose of tongues in the New Testament. The quotation from Isaiah 28 is completely inappropriate if the message of the tongues (language) utterance is misunderstood.
tongues are for a sign,
There is a definite article before the word “tongues” in Greek, giving tongues pointed specificity, and thus refers to the Isaiah 28:11-12 quote of the previous verse. The tongues of which Paul spoke are true languages.
Jews were “sign” hungry in Corinth, for the Jews required a sign (1 Co 1:22). They wanted signs and wonders to prove things. Jesus lamented that as well. “Sign” (semeion) has particular use in the New Testament as a miraculous authenticating pointer, a sign of something miraculous. The word “sign” carries the idea of signal, standard. A sign is something that distinguishes something, a sign of God’s approval. A sign was a miracle that authenticated a special message. Jesus gave “signs” of his deity in the gospel of John (Jn 20:30-31). A sign was more than a miracle; it was a miracle that pointed to a message. Tongues were a God-given sign to the Jews that New Testament truth is true.
not to those who believe but to unbelievers;
There is a definite article “the” before “unbelievers” in Greek. This definite article points back to the unbelieving Jews in verse 21 (an article of previous reference – this is a classical article of previous reference because it follows a quote). These “unbelievers” were not merely unsaved people but unbelieving people who had doubts about the message proclaimed. The unbelieving Jews of Isaiah 28 were in a condition of unbelief or negative volition. “The unbelievers” were the Jewish people who rejected Isaiah’s message and the Jews who rejected Paul’s message. God deplores this condition of unbelief – “and yet for all that, they will not hear me.” The entire purpose of tongues arose directly from Scripture. The Jews’ need for confirmation of New Testament revelation resulted in the manifestation of the extraordinary sign gifts of speaking in a foreign language without studying it.
Paul’s purpose was to preserve the gift of tongues as a sign to unbelieving Jews. Every one of the four occurrences of speaking in tongues in Acts was to unbelieving Jews (Acts 2; 8; 10; 19). Tongues are definitely not for the benefit of believers but were meant for unbelieving Jews at the time of the founding of the church.
Ac 2:36, “Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ.”
Ac 10:45, And those of the circumcision (Jews) who believed were astonished, as many as came with Peter, because the gift of the Holy Spirit had been poured out on the Gentiles also. 46For they heard them speak with tongues and magnify God.
Ac 18:5, When Silas and Timothy had come from Macedonia (to Corinth), Paul was compelled by the Spirit and testified to the Jews that Jesus is the Christ (Messiah).
Ac 19:8, And he went into the synagogue and spoke boldly for three months, reasoning and persuading concerning the things of the kingdom of God.
but prophesying is not for unbelievers but for those who believe.
Today prophecy is the gift of exposition and benefits only believers. It is not for obstinate Jews. Before the closing of the canon, prophecy carried the idea of new revelation content.
The purpose of speaking in foreign languages (tongues) was to prove to the Jews in the first century that the New Testament was the authentic Word of God.
The purpose of speaking in tongues was as a sign to unbelieving Jews that the message of the New Testament was true and that they could believe the message of the apostles in the first century.
The gift of tongues ceased when God authenticated the New Testament as true. Its purpose was fulfilled through clear evidence that God spoke through New Testament apostles in the first century. The destruction of Jerusalem in A.D. 70 signaled that God turned His attention to the Gentiles (Lu 21:20-24). Today God’s purpose for the Jews is now in abeyance, and His purpose for the Gentiles is in the ascendancy.