1 Corinthians 1:10-12
There is no doubt that the church is now badly divided—and it shows no evidence of reuniting—yet we are all commanded to speak the same things.
Paul goes on to use the words "mind" and "judgment." Mind is actually related to the power of observation—the way that we see things. He is saying we all need to see things in the same way. Judgment deals with the forming of an opinion.
The Corinthians obviously did not all see things the same way, and they therefore could not possibly come to the same opinion. So they did the natural thing and divided. They did not actually leave the congregation, but cliques formed within it, and the members were not at peace with one another.
Why did they not see things the same way? The context shows it depended upon whom each person decided he would use as his authority. Some used Paul, some Apollos, some Peter, and of course, some Christ. There is no evidence that those named as authorities were divided, but people made it seem so. No wonder they were divided! Today, sadly, many are doing the same thing.
John W. Ritenbaugh
Unity (Part 2): God's Pattern of Leadership

The church is badly divided yet all are commanded to speak the same thing with no divisions, being perfectly joined in the same mind and judgment. Mind relates to seeing things the same way while judgment involves forming the same opinion. Divisions occur when people choose different authorities such as Paul, Apollos, Peter, or Christ, creating cliques without leaving the congregation. Obeying a person contrary to God's direct commands constitutes idolatry. Speaking the same thing is a commanded choice for unity by following Christ.