Click here to read what the Bible says about unity for believers.
Now I plead with you, brethren, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no divisions among you, but that you be perfectly joined together in the same mind and in the same judgment. - 1 Corinthians 1:10
Unity is being of the same mind, beliefs, and morals. As Christians and fellow brothers and sisters in Christ, we are commanded to be unified. The Bible says that we are one body in Christ with many members. One body cannot have different beliefs, values, or morals, all body parts work together to make the body productive and healthy. Each member has an important role in the body of Christ, we all have different skill sets, talents, and gifts that are to be used to glorify God, honor the Church, and encourage and admonish one another. When we work together and are in unity then the body does well and God is pleased. However, when we are split or in disunity then it gives the devil room to harm the body and for sin to creep in. There are many churches, they are earthly churches, but there is only one Church, and that is the body of Christ which is the unity of true believers.
The elders who are among you I exhort, I who am a fellow elder and a witness of the sufferings of Christ, and also a partaker of the glory that will be revealed: Shepherd the flock of God which is among you, serving as overseers, not by compulsion but willingly, not for dishonest gain but eagerly; nor as being lords over those entrusted to you, but being examples to the flock; and when the Chief Shepherd appears, you will receive the crown of glory that does not fade away. - 1 Peter 5:1-4
This does not mean we have to