Why is sound doctrine essential for the unity of the church?

Sound doctrine is essential for the unity of the church because the only true unity is unity in the truth (1 Jn. 1:1-4; 2 Jn. 10-11).

Think about it. Without sound doctrine the church will be a jumbled mess of everyone’s personal beliefs. If the church without sound doctrine is united, it will either be united around whimsical sentiment or an explicit untruth. In either case:

• The church won’t be able to evangelize. If the church has no agreement about the gospel, or unites around a false gospel, it won’t be able to proclaim the true one.
• The church won’t have a biblical understanding of what it means to be a Christian.
• The church won’t have a biblical understanding of who should or should not be a member of the church.
• The church won’t agree about who to worship, or how they should worship, or why.

In short, sound doctrine is essential for the unity of the church because the church is the people created by the gospel. If the gospel is not proclaimed, taught, and defended, the church will soon cease to be a church at all, much less a united one.