One of the saddest things in Christian life is when you meet or hear about people, sometimes within the same church who have not spoken for years. Similarly you can even discover churches where there has been rivalry going on since a split decades ago.
Sometimes Christians will disagree sharply. The Apostle Paul disagreed with his brothers, fellow leaders and even other apostles. There are two particular stand-out examples. In Acts 15:36-39, Paul has a sharp disagreement with his co-worker Barnabas. Paul is concerned that Mark has proved unreliable in ministry and so does not want to take him on a further mission trip. Barnabas wants to give Mark a second chance. The two missionaries disagree, sharply, and go their separate ways. It was not a great witness for the Gospel.
However, in Colossians 4:10, Paul tells the church to give Mark a warm welcome. The rejected missionary has become an essential friend and companion to Paul. Given that Mark is described as a cousin of Barnabas (which might explain the loyalty shown to him), it is reasonable to assume that there has been reconciliation with Barnabas too.
In Galatians 2:11-21, Paul is once more in dispute, this time with Peter (Cephas). Peter has withdrawn from table fellowship with Gentiles and Paul publicly rebukes him to his face because he sees Peter undermining the very Gospel that both men are united together in. Yet it is also clear from how Paul writes about Peter in Galatians 2 that he continues to esteem the other apostle, and he recognises him as one of the first witnesses to the resurrection in 1 Corinthians 14:5. Meanwhile, when Peter writes about Paul, he describes him as “our dear brother” (2 Peter 3:15).
There may be times when we fall out with a fellow Christian. Usually, it will be a source of great distress to people. It is not a good thing when Christians fall out but sometimes the cause will be a serious disagreement where it is right to take a stand for truth. However, our aim should be to ensure that disagreements don’t lead to long term fall outs. We should not bear grudges and we should seek reconciliation and to make peace when there has been a falling out.