The above passage is critical for the life of the church. We read Paul begin to exhort us to "walk in a manner worthy" of our calling. In the preceding three chapters of Ephesians, Paul emphasizes the wonderful things God has done in salvation. In chapters 4-6, Paul instructs us in how to live our lives in light of all God has done. This is walking worthy of our calling.
Paul takes a few verses to begin to explain what this walk looks like as we relate to other Christians. We are to show humility, gentleness, patience, and bear with one another in love. The apostle then stresses the importance of unity within the body. Paul discusses the unity of various aspects of the Christian faith and life. In verses 4-6 alone, Paul uses the word "one" on seven different occasions. Paul's redundancy has a point: to stress the absolute importance of the unity of Jesus Christ's church. He even brings the members of the Trinity into it: One Spirit, One Lord, One God and Father.
As we think about the church, this passage must inform both what we believe and how we act. We make a mistake if our focus falls simply on the unity of our own local church body. It is relatively easy to be united with people we agree with, know, and love. Paul's admonition goes far beyond this. As followers of Jesus, we are to be united with all other Christians. We are to be one with them.
This may seem like a tall order since we may disagree with many other Christians about a great many things. However, since they are Christians were are automatically united in the gospel of Jesus Christ. The things that might seem to divide us (such as the ordinances/sacraments, spiritual gifts, church polity, church structure, view of children, etc.) really should not separate us in any way.
This means that we should always be ready to meet other Christians and rejoice with them over being one in Christ. This may happen when the church gathers, but it may also happen in the grocery store, over the back fence, in the bank, over the internet, in the park, at the office, or wherever. Unity in Christ spans location, socio-economic status, education, income, background, etc.
Let us therefore go out of our way to be united with all other followers of Jesus Christ. This may take different forms on different days. It will, however, always be joyful.
In human terms, it may not seem possible for people who disagree on important issues (for example the meaning of baptism) to be united. In response to this disagreement, we often in reality divide while at the same time giving lip service to unity. We don't gather together, but in theory say we are united. This is simply unbiblical.
If we are in Christ and someone else is in Christ, then we are united in Him. Therefore, we must act like it. Let's then do all we can to foster this unity. Let's meet others wherever they are and encourage them and be encouraged. It should be exhilarating to spend time with with other believers if the aim is to build one another up in Christ.
Let's focus on what unites us (Christ) instead of what may divide us (secondary issues).
Division is disobedience. Division is sin.
Unity in Christ is obedience. Unity in Christ is God-glorifying.