These words of the apostle Paul regarding the use of Spirit-given languages (“tongues”) and prophecy in the Church may seem completely contradictory. Paul initially says that tongues are a sign to those who are unbelievers, and that prophecy is given for believers – for those in the Church (verse 22). But then, in the following verses, Paul continues with an example in which he says that if an unbeliever comes to a church and hears people speaking in unintelligible speech the outsider will thinks that they are out of their minds. On the other hand, Paul says, if the unbeliever comes in and the church is prophesying then he or she will be convicted and will worship God.
The key to reconciling this seeming contradiction between the point Paul makes, and the example he gives, is found in understanding that Paul means tongues are a sign to unbelievers, not to their conviction and belief, but to confirm their unbelief. We see this in what he says in the verse directly before those we are looking at: “In the Law it is written: ‘With other tongues and through the lips of foreigners I will speak to this people, but even then they will not listen to me,’ says the Lord.” (verse 21).
In other words, tongues are a sign to the unbelieving, not that they might believe, but that they are condemned in their unbelief in not turning to God so that they might understand. Understood this way, there is in fact, no contradiction. Tongues are a (negative) sign to unbelievers, while prophecy – which Paul is stressing in this chapter is more important than tongues (verses 4–5; 19) – is a (positive) sign to believers. On the other hand, if unbeliever’s hear words they can understand (prophecy) they may be convicted and converted, Paul says. While tongues sometimes serve to strengthen unbelief, prophecy serves to strengthen belief.
The context of these verses makes this all clear. The Corinthians were misusing the gift of tongues so that there was no benefit to the church in their use. Tongues used this way – without interpretation (verses 13; 27–28) – were not of any use to believers or unbelievers alike. Prophecy on the other hand, was helpful to those in the church because it conveyed the word of God to them, and even unbelievers, Paul reminds them, might be instructed and brought to faith by an intelligible message that convicted them of sin by revealing “the secrets of their hearts,” and helped them to see God's indwelling presence in the church (verses 24-5).
In this example, as in other parts of Paul’s writings, we must be aware that the apostle often appears to say one thing but then another as he looks at issues from different angles. This is no different from us saying that someone is too short when it comes to playing basketball, but not short enough to be good at gymnastics (where being shorter and having a lower center of gravity is actually an advantage). Paul has sometimes been called the most difficult of the apostles to understand (2 Peter 3:16) but we can better understand his writings by always keeping in mind the flexibility of his thinking.