If the Spirit is not divided against itself, then why are there so many denominations? -Gordon
A denomination does not mean a division in the Spirit. Paul and Barnabas had a disagreement once about how to deal with fallen recruits and so had to begin different ministries. Does that mean that the Spirit was divided? No, it meant that the Spirit wanted to work differently with each of them. Paul was going to the "front lines" in a severe ministry, and weak believers just couldn't do that ministry. It would have been wrong for Paul to compromise his ministry for the sake of someone who wasn't ready to participate in it. But should Barnabas have listened to Paul? No, his task in the Spirit is to bring up the weak and encourage them. Because of Barnabas, John Mark became the strong disciple he turned into. Different ministries were necessary at that point.
Even so, the denominations. God allowed the divisions so that the church might be strong in different areas. If it weren't for the minority Pentecostal movement, there would not have been the powerful move of the Spirit over the last hundred years. If it weren't for Luther, there wouldn't have been such an emphasis on the Bible for the last four hundred years. If it weren't for the Mennonites and Moravians, there wouldn't have been Protestant Christian communities. God established these divisions to allow the Spirit more movement to work.
Of course, sometimes divisions turn ugly and there is backbiting, gossiping and every other kind of terrible disunity. God did not cause that, but people's self-centeredness and narrow-mindedness did. Disagreements need to be guided by Galatians 5-- not of the works of the flesh, but of the fruit of the Spirit. Only then will division and denominations agree to go in different ways, but still remain unified in the Spirit.