Therefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying serves not for them that believe not, but for them that believe.
All Commentaries on 1 Corinthians 14:22 Go To 1 Corinthians 14
Ambrosiaster
AD 400
The utterances of God are hidden beneath the veil of an unknown tongue, so that they should not be seen by unbelievers. Paul was saying that tongues are useful for hiding ideas from unbelievers. Commentary on Paul’s Epistles.