I left a comment similar to this on facebook, and I thought I would add it here too:
The differences that I and another believer have are subordinate to the covenant which unites us (that would be our mutual covenant/relationship with God, not a covenant that we devise between ourselves). In many ways differences between believers actually serve that unity. However, we can allow our differences to separate us when we attempt to base our unity in our common doctrines, dogmas, or beliefs.
Our unity is found in our common relationship with God. Since God is our Father, then we are brothers/sisters. We do not have to create this union, we only have to live according to it, such that we do not allow our differences to become more important than our mutual family relationship.
“Doctrines” and “dogmas” are different teachings that must be subordinate to our mutual relationships. Of course, as Paul, Peter, and others point out in Scripture, there are some beliefs that demonstrate that we are NOT brothers and sisters (i.e. a doctrine that God does not exist, or a belief that Jesus is not the son of God, etc.). However, for those we recognize as brothers and sisters because we recognize that Christ has accepted them (Romans 14:7), then we are bound by our relationship with God to accept them as brothers and sisters as well, and to treat them as brothers and sisters.
Today, we tend to acknowledge that someone is a brother/sister (Christian) based on the mercy and grace of God, but we only treat someone as a brother/sister based on their doctrines, dogmas, or beliefs. However, according to Scripture, if we acknowledge someone as a brother/sister based on the mercy and grace of God, then we must also accept that person as a brother/sister and treat that person accordingly.