One of Jesus' primary concerns was for his disciples to live and function in unity. Unity is not uniformity. Unity does not mean we live, act, dress, or speak the same. Just as love demonstrates we follow Jesus, our unity demonstrates God sent Jesus, and God is for us. There is some scripture that links love with unity. So, it is not too hard to recognize how unity testifies to the truth of Jesus.
One metaphor used to describe the church is the human body. Each person isa part of Jesus' "body." Just like the physical body, the part s of Jesus's body have different functions. The functions are intended to maintain the health of the body. As I have written before, I believe the functions within the body of Christ are better defined as to build the kingdom, because some parts have the function of interacting with the environment, other people, and the culture. These functions are not intended to be focused internally. The Bible calls these functions "spiritual gifts."
The concept of spiritual gifts got lost for several centuries between Jesus's time and our time. Of course, in God's economy, there are things that are more important than gifts. (Love is vastly more important than gifts. I think gifts are a subset of love. Each person's gift is a way God has given them to demonstrate love to others.) When it was re-discovered, there was understandably a lot of confusion and ignorance. This was a new thing. There are more theories about what gifts are, how they are to function, how they are gotten, and how important they are in the overall scheme of things. And people disagree. And what God gave to express love and unity does the opposite.