Unifying the church is a hard work because it involves relationships. Of course, this also means that when done right, it is one of the most satisfying works because of the good relationships between brethren.
How is unity accomplished? Unity must be in the faith (Ephesians 4:13). That rules out the unity that we see in the denominational world of just saying that even though they disagree about a lot of very important things, they can still work together. That is not true unity.
Unity also does not mean that we have to agree on everything (although that is a goal to shoot for — that we would all understand the will of God perfectly). But the truth is that there are always going to be disagreements among brethren. What should we do about them?
The principles found in Romans 14 are very important for us to understand and implement. Verse 13 says,
Therefore let us not pass judgment on one another any longer, but rather decide never to put a stumbling block or hindrance in the way of a brother. (ESV) This is talking about doing things that your brother thinks are sinful where you might be influencing him to sin against his conscience and so sin against God. In verse 16 it says,
So do not let what you regard as good be spoken of as evil. (ESV) This does not mean that if someone tells you that eating meat is sinful, you should tell him to shut up. This means that if someone believes that what you are doing is sinful, you stop doing it! How can you edify your brother if you thinks you are continuing in sin? Do you really think he will listen to you or follow your example in anything else?
If we are to have unity, it means giving up what we want when our brethren believe it is sinful. Division has happened many times in churches because brethren did not follow this principle. An example is when musical instruments were brought into the worship services. There were many who objected that they were unauthorized and therefore sinful, but those who wanted them brought them in anyway and those who objected had to leave or sin. There was no love there and certainly no unity. The same thing happened when churches involved themselves with organizations like orphan homes, colleges, and others. Those who wanted them forced those who did not want them to leave or sin against their consciences.
Warn a divisive person once, and then warn him a second time. After that, have nothing to do with him. You may be sure that such a man is warped and sinful; he is self-condemned. (Titus 3:10-11) (ESV)
It is these who cause divisions, worldly people, devoid of the Spirit. (Jude 1:19) (ESV)
Causing division because we are determined to have our own way is a warped and sinful way of thinking and living. We must be careful. Unity is important to Jesus and He will not hold us guiltless who cause division in His body.