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.

Tongues in a church are not a sign of God's blessing at all, any more than the foreign tongue of the invader was a blessing of God in Jerusalem, but just the opposite! Tongues in a church? Not as long as there is a single believer in it! The notion that speaking in tongues is to convert unbelievers is foreign to this text. It does just the opposite of converting unbelievers, with the result that they turn aside in disgust, as Paul stated in the very next verse.

Prophesying a sign ... to them that believe ... The fact of Paul's calling it a "sign" for believers instead of saying that it was merely for the benefit of believers indicates that the miraculous endowment of certain teachers in the primitive church is in view. It must have been of great value to have such directly inspired teachers in that age of the church (the infancy age); and the foolishness of the Corinthians is seen in their astounding preference for the showy gift of tongues, instead of honoring and preferring a gift that could have blessed and benefited.