When we look to the bible, we see very clearly that the dividing line is the gospel.
In Galatians 1:8-9, Paul writes, "But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed."
When we look to John 17, we very clearly see Christ's desire for the unity of His church. In John 17:20-23, Jesus prays, "I do not pray for these alone, but also for those who will believe in Me through their word; that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us, that the world may believe that You sent Me. And the glory which You gave Me I have given them, that they may be one just as We are one: I in them, and You in Me; that they may be made perfect in one, and that the world may know that You have sent Me, and have loved them as You have loved Me."
So, according to the scriptures, it is the gospel that unites brothers and sisters in Christ. Technically speaking, of course, it is God Himself who unites us and is our Father. His gospel is the way that we are united. This is God's plan.
The bible speaks of NO secondary doctrines around which we should divide from other Christians. We are never told to divide over issues such as baptism, the Lord's Supper, spiritual gifts, church polity, views on predestination/free will, bible versions, etc.
When churches in the N.T. (see Corinth and Philippi for example) were dealing with division, Paul told them to stop it. Division over issues lesser than the gospel is always seen in a negative light in the N.T.
Today, however, our churches are splintered into many different denominations. Some of this needs to take place because some denominations have rejected the gospel. However, there are also many denominations that adhere to the gospel yet remain divided.
For example, many Christians refuse to meet with one another because they hold different beliefs on baptism. Baptism is certainly an important issue. However, the bible nowhere even suggests that we should separate over it. The same can be said for a whole host of other issues.
Some Christians will say that they really are united, but just don't gather together. I find their reasons for not gathering together to be completely pragmatic and unbiblical.
What is a better way? My suggestion is that we, as Christians, unite around the gospel of Jesus Christ. Based on this and this alone will we unite or be divided. We should make this clear and be firm about. Let us agree that nothing sub-gospel will divide us.
Basically, we will be saying that while we may disagree on some things, we will still be united.
Once we make this decision, then we will be forced to start talking through some of these other issues. As we do so, we will gain deeper understanding of why others believe differently than we do about issues such as baptism, spiritual gifts, etc. We may come to gain greater respect for their positions, even if we still disagree with them. The more we talk, the more likely we are to find that our positions are closer than we thought.
Division within the church is, quite simply, disobedience. God expects His children to be united.
I hope denominations eventually go the way of the Dodo Bird.
Unity is not an option. Let's embrace our unity in the gospel of Christ.