Many think that genuine oneness is based on doctrinal agreement. So, for instance, we have been criticized for teaching wrong doctrine because of a difference in the interpretation of the sign of the woman in Revelation 12. How could Christians ever be one if it required agreement on every detail of doctrine? There are certain items of the faith, especially concerning the person and work of the Lord Jesus, which are crucial to our acceptance by God. These distinguish believers from unbelievers and we cannot compromise them. But there are many other items to which we need to apply the principle found in Romans 14 and receive our fellow believers without trying to convince them that our understanding is correct.
Similarly, Christians need to pray, read the Bible, meet together, etc. The ways they do these things become their practices. But Christians have had real experiences with the Lord and have even developed deep personal relationships with Him through many different practices. Whenever we insist on a certain practice we cut ourselves off from other real believers. Of course there are practices which we cannot accept because they are sinful or idolatrous but we need to be careful not to reject things simply because they do not match our background or taste. The point is that the real oneness in Christ is not based on similarity in practice.
Thirdly, oneness is not based on a certain measure of growth in life. Some of us have been living, meeting and serving the Lord together for many years. We know each other's strengths and weaknesses sometimes better than we know our own. Can we reject those whose growth does not correspond to the number of years that they have known the Lord? If so, then there are many believers with whom we cannot be one.
The real oneness in Christ is not based on anything outward; it is Christ Himself. In practice, this means that in many things we need to be flexible and tolerant of others.