Note 26 at 1 Cor. 14:22: Speaking in tongues is a sign to unbelievers, not believers. Usually a sign is a positive thing which helps people believe (see note 2 at Lk. 2:12, p. 54). But there are also negative signs which were intended to be a stumbling block to those with hardened hearts (see note 10 at Mk. 6:52, p. 238 and note 3 at Mk. 8:17, p. 258).

Simeon prophesied over Jesus at His circumcision in the temple that Jesus would be a sign that would be spoken against (Lk. 2:34). Isaiah also prophesied that the Messiah would be, "a stone of stumbling" and "a rock of offense," "a gin" and "a snare" (Isa. 8:14). These prophesies certainly came true in many people's lives. Isaiah also said, in the scriptures which Paul had just quoted (Isa. 28:11-12), that despite this miraculous manifestation, "they would not hear."

Therefore, speaking is tongues is a negative sign to unbelievers that will cause them to think we are crazy (v. 23). That's the point Paul is making and that is the reason why he is telling them not to speak in tongues in church in a way that dominates the assembly (see note 13 at v. 28, p. 950).

Some one might say, "but the disciples spoke in tongues on the day of Pentecost and 3,000 people were saved" (Acts 2:41). But those tongues were the known languages of the people who were listening. Tongues with an interpretation equals prophecy (see note 12 at 1 Cor. 14:5, p. 944). Since those tongues were able to be interpreted by the hearers, that had the same positive effect that prophecy has (vv. 24-25).

So, Paul quotes Old Testament scripture to verify that tongues are a negative sign that will cause unbelievers to reject our witness. This was done to persuade the Corinthians not to speak in tongues in church without an interpretation.

Note 27 at 1 Cor. 14:22: This verse is simply saying that tongues has a negative effect on unbelievers (see note 26 at this verse) while prophecy has a positive effect on those who will believe.