What does 1 Corinthians 14:19 mean?

Paul has thanked God, in the previous verse, that he speaks in tongues more than anyone in Corinth. Since he spent so much time with them when founding the church there, they may know this fact well. Paul's restriction on the exercise of the gift of speaking in foreign languages in church without an interpreter is not from jealousy. He, too, has the gift and uses it.

The difference between Paul and the Christians in Corinth is in how and when he exercises the gift of speaking in tongues. He has shown in this chapter that all spiritual gifts are given for building up the church, by Christians building up one another. Speaking in tongues when nobody else knows what is being said does not help with that.

To show how seriously he means this, Paul now adds that he would rather speak five words formed in his mind to teach others in a church service than to use 10,000 words in a language neither he nor anyone else could understand. Those five words, understood by all, serve the purpose of the church, while 10,000 words without meaning serve no purpose, at all.