Childish—that term describes the way that the first-century church at Corinth acted with respect to spiritual gifts. Just as children are prone to show off, the Corinthian believers treated the gift of tongues as something to be paraded before others. Multiple members were all exercising the gift at once during the worship services, leading to much confusion (1 Cor. 14:23). Perhaps some of them boasted that they spoke in tongues more than others, which Paul may be countering when he notes his own use of tongues (v. 18). They did not understand the superiority of intelligible speech in the corporate assembly to words that could not be understood, just as children often are unable to prioritize things properly (vv. 1–19).
Since childishness was the problem in Corinth, the way to get back to the right use of spiritual gifts was for the Corinthian believers to grow up. Thus, Paul calls them in today’s passage not to be children in their thinking (v. 20). In other words, they were to develop the capacity to reason properly and think through matters completely, which is one of the traits of adulthood. As John Calvin comments, “Paul would have all believers to be, as far as possible, in full maturity as to understanding.”
The New Testament, of course, frequently exhorts us to be like children. For example, Jesus says we must become as little children to enter the kingdom of God (Matt. 18:3). The Apostle’s exhortation to give up childishness in our thinking does not contradict this. Jesus commends becoming like children not in every sense but in the sense of having the same relationship of utter dependence on the Lord that young children have on their parents. Indeed, even Paul commends childlikeness in certain ways. He also tells us in today’s passage to be infants with respect to evil (1 Cor. 14:20). That is, we are not to have the same experiential knowledge of evil that people gain as they grow up and become experts in sinning. Instead, we are to be like children who are “unskilled,” as it were, in the practice of sin despite the fact that they are sinners. Young children can and do sin, but they are unable to do many of the sins associated with adulthood. Believers should imitate them in this.
In our thinking, however, we are not to be like children. We must grow up in our understanding of God and His Word and its application. This is what it means to be mature in our thoughts (v. 20).