New Revised Standard Version
Tongues, then, are a sign not for believers but for unbelievers, while prophecy is not for unbelievers but for believers.

Contemporary English Version
Languages others don't know may mean something to unbelievers, but not to the Lord's followers. Prophecy, on the other hand, is for followers, not for unbelievers.

New American Bible
Thus, tongues are a sign not for those who believe but for unbelievers, whereas prophecy is not for unbelievers but for those who believe.

Douay-Rheims Bible
Wherefore tongues are for a sign, not to believers but to unbelievers: but prophecies, not to unbelievers but to believers.

Wherefore tongues are for a sign, not to believers but to unbelievers: but prophecies, not to unbelievers but to believers.

for a.

Mark 16:17 And these signs shall follow them that believe: In my name they shall cast out devils. They shall speak with new tongues.

Acts 2:6-12,32-36 And when this was noised abroad, the multitude came together, and were confounded in mind, because that every man heard them speak in his own tongue. . . .

not to.

1 Timothy 1:9 Knowing this: That the law is not made for the just man but for the unjust and disobedient, for the ungodly and for sinners, for the wicked and defiled, for murderers of fathers and murderers of mothers, for manslayers,

but for.

1 Corinthians 14:3 But he that prophesieth speaketh to men unto edification and exhortation and comfort.