One of the hallmarks of Christianity, especially in the local sense, is unity. N.T. passages like Rom. 12:16 and 1 Cor. 1:10 come to mind, exhorting disciples to "be of the same mind." We share goals and aspirations with those "of like precious faith" to which others in the world cannot relate.
Jesus did pray for all His disciples to be unified (Jn. 17:21). Paul wrote we should "be diligent to preserve the unity of the Spirit in the bond of peace" (Eph. 4:3). However, we are all still people. We're not programmed like robots once we obey the gospel. We still have distinct personalities and opinions that comprise our character. There will be times when good-hearted brethren will differ over matters as they pertain to our work together. We can read about one such occurrence in Acts 15:36-40.
Paul & Barnabas had been sort of a "gospel dynamic duo." After being set apart together by the Holy Spirit for their work (Acts 13:2), they traveled a good bit in the ancient world doing the work of the Lord. As you read Acts 13-15, imagine all they experienced together. No doubt they had developed a close bond of trust and dependence upon each other. They knew the other would be there in times of need. All of a sudden - BAM!! Now there is a rift.
Paul suggests they return to every city where they had planted a church and see how the brethren are doing (v. 36). Barnabas agrees, and wants to take John Mark. Paul doesn't like the idea, reminding Barnabas how Mark had previously let them down (vv. 37-38; cp. 13:13). What resulted was a "sharp disagreement that they separated from one another" (v. 39a). Barnabas did take Mark and went his way while Paul chose Silas and went his (vv. 39b-40). We have no further information that Paul & Barnabas ever teamed up again.
Was Paul being petty, vindictive? Was Barnabas too soft? Neither. It was simply a disagreement over how to get the Lord's work done. Did Paul ever get over "his problem" with Mark? His remarks in Col. 4:10 & 2 Tim. 4:11 indicate he held no grudge.
Good brethren can disagree about how God's work should get done. What we must focus on is not letting the disagreement overshadow the work. That we cannot afford to do.
