Within Christianity, there are many groups that divide over very specific things outside of the Gospel of Salvation and deity of Jesus (I John 4:2-3). This page explains why those groups exist and how they can unite.
Endorsements
Many Christians have sought theological unity, such as Martin Luther, Billy Graham, and various popes.
Concepts
Why did God allow denominations?
Although denominations are allowed (Romans 14:3) and decentralized churches are encouraged (Mark 9:38-39), many would agree it’s not ideal for unity (I Corinthians 1:10). God allowed these divisions because they allowed various truths about God to flourish and not die out due to church pride. Evangelicals boldy preach the Word (II Timothy 4:2) and have a personal relationship with Jesus (John 15:15). Charismatics ecstatically pray to the Holy Spirit (Jude 1:20) and prophecy into others’ lives (I Corinthians 14:1). Catholics revere the Holy Father in the Eucharist (Luke 22:19) and evangelize as the largest denomination (II Timothy 4:5). Orthodoxy’s rich history stays true to their soul (I Corinthians 11:2), and are loyal through baptism to the King (Acts 8:12).