What should you do if you see someone sinning? In our culture, the typical answer to that question is, “Absolutely nothing!” There are several reasons for this answer.
For one thing, we have drunk deeply from the cup of John Stuart Mill. In 1869, Mill published an influential essay, On Liberty, which advocated “one very simple principle”: “the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection.” In other words, if you see someone sinning, unless he is sinning against you, leave him alone.
For another thing, we have eaten at the table of moral relativism. That ideology teaches that the commandments, “Thou shalt” and “Thou shalt not,” are relative to the culture or the individual that commands them. What is cannibalism in one culture is another culture’s four-course meal. One man’s pornography is another man’s art.
There’s a bit of truth in both of these reasons for doing nothing, but only a bit. Christians are neither competent nor capable to intervene in every case of wrongdoing. If we tried, we wouldn’t have time to do anything else. And anyway, sometimes we do confuse morally universal norms with culturally relative practices. Marriage is a moral norm; wearing a white dress to a wedding is a cultural practice. We’d look silly if we imposed white dresses on a culture that had a different color scheme for weddings.
With these qualifications in mind, however, there are times when we are obligated to do something when we see someone sinning. The question is really not whether we should do something, but what we should do and when. First John 5:16-17 provides Christians with guidance on answering these two questions.
If anyone sees his brother commit a sin that does not lead to death, he should pray and God will give him life. I refer to those whose sin does not lead to death. There is a sin that leads to death. I am not saying that he should pray about that. All wrongdoing is sin, and there is sin that does not lead to death.
Regarding what, John advises us to pray. Other Scriptures advise us to stage an intervention of some sort. (See Matthew 18:15-17, Galatians 6:1-2, and James 5:19-20, for example.) But here, John counsels us simply to bring the issue before God in humble supplication. We may not be competent or capable of intervening, but God is. So pray!
Regarding when, John advises us to intervene in the case of a “brother,” that is, a fellow Christian. As Christians, we know what is on the line with sin, namely, life and death. Repentance leads to life. Lack of repentance leads to death. If you love your brother or sister, you will pray for their repentance.
As Christians, when it comes to the sins of others, God does not call us to either busybody-ism or indifference. But he does call us to concern. And the first expression of concern is always prayer.