In the second half of 1 Corinthians, Paul makes a bold proclamation about this church, "There must, indeed, be factions among you, so that the approved among you may be recognized." (11:19) In a book filled with correction, it is a good consolation to know some in Corinth who were approved by God! That means they tolerated neither the sins happening in the church nor the doctrinal errors being espoused by some. These "approved" Christians didn't divide about which teacher was best; they divided in a way God approved of.
In fact, Jesus prophesied that the gospel would cause a similar kind of division, "Do you think that I came here to bring peace on the earth? No, I tell you, but rather division. From now on, five in one household will be divided: three against two, and two against three." (Luke 12:51-52) This means that the gospel fundamentally changes families. Some will believe, others will not, and that will cause division. Regardless, nothing, not even earthly family, is more fundamentally important than staying true to Jesus Christ. And God's people may undergo even the rejection of their closest kin as they stay faithful to Jesus Christ.
What counts as a justifiable division in the church?
While it's fresh on our memory, let's look again at 1 Corinthians 1:10, "Now I urge you, brothers and sisters, in the name of our Lord Jesus Christ, that all of you agree in what you say, that there be no divisions among you, and that you be united with the same understanding and the same conviction."
To remedy the church's needless divisions about teachers, Paul teaches that the church must unite in three ways: 1) "what you say", 2) having "the same understanding", and 3) having "the same conviction".
We have an example of the first kind of division in 1 Corinthians 15:12, "Now if Christ is proclaimed as raised from the dead, how can some of you say, 'There is no resurrection of the dead'?"
If you read ahead in that chapter, you will see that Paul doesn't go on to say, "That's fine as long as you don't get too divisive about the way you say it." Nor does he say to those on the other side, "You who believe in the resurrection should accept these people, regardless of their view of the resurrection."
In fact, he says that those who deny the resurrection are completely wrong and that they are undermining the entire Christian faith. Some might say Paul is downright narrow-minded when it comes to the resurrection. But that's because, well, so is God.
The second kind of unity is based on a shared understanding. The word for "understanding" is the Greek word that means "mind". What is the mutual "mind" that we must share?
Paul states that in 1 Corinthians 2:16, "For who has known the Lord’s mind, that he may instruct him? But we have the mind of Christ." Through the Spirit and the word of God, we have access to the truth that comes to us directly from the mind of God. About his own writings, Paul says, "We also speak these things, not in words taught by human wisdom, but in those taught by the Spirit, explaining spiritual things to spiritual people."
So the entire church can have unity of understanding by submitting to the Spirit's leading in the Bible.
The third kind of unity the Corinthians need to have is a unity of shared "conviction". This is the Greek word "gnṓmē" which occurs two other times in the book (7:25 and 7:40) and is translated "opinion" there.
The word "opinion" is misleading because many will think Paul is referring to his own private musings. In reality, the word is being used here more like a courtroom opinion that a judge issues in deciding a case. I appreciate how the ESV translates this word more directly as "judgment". In both 7:25 and 7:40, Paul is giving a God-given judgment about how betrothed couples and widows should respond to their unique situations.
When Paul says that the church should have the same "conviction" or "judgment", he's saying there should be unity about what kind of behavior is good and what is not. There is a serious lack of good judgment at Corinth. Immorality, lawsuits, prostitution, and paganism are being sanctioned by many in the church because of a lack of sound judgment.
If you put it all together, Paul is saying that the church (then and now) must have 1) an unequivocal stance on the doctrines that comprise the gospel, it must 2) agree to submit to the Bible, and it must 3) stand firm against sin and for obedience to God.
For Christians, these categories address issues that are legitimate reasons for division within the church.
Now, this teaching is very helpful to us because some Christians may be fearful of being too divisive while others may be overzealous in their willingness to divide fellowship.
If you err on the side of being too divisive, recognize that not all doctrines are equally important. Of course, everything the Bible says is important. But someone can be saved without understanding the correct mode of baptism; they can't be saved without knowing that Jesus died for our sins. So if you are divisive beyond what Scripture tells you to divide over, you create more problems than you solve. Don't place all doctrine on the same level of importance. There are many noble hills for a Christian to die on. Commit your ways to the Lord and let Him direct your boldness to the doctrines that matter most.
If you err on the side of timidity, understand that standing up for these core truths of the gospel could lead a false-professing Christian to true faith in Christ. Your boldness could expose an error that prevented someone from knowing God. There is nothing more loving than patiently exposing an error so that someone can truly know God.