Ephesians 4:3 exhorts us to keep the oneness of the Spirit in the uniting bond of peace. But what does this mean practically? As a young Christian I used to sing about being one in the Spirit but practically I was not one with other believers and I had no idea how Christians could really be one. My concept was that we should seek to teach and live according to the truth in the Bible as we understood it. I don't think believers would disagree with this but I had no idea how wide a door this concept left open for Satan to damage the church through division. Christians who only held to this concept with no idea about how important it is to keep the oneness would naturally align themselves with those with whom they agreed and separate from the ones with whom they disagreed.
The main shortcoming of this concept is that it makes no distinction between the small number of crucial items of the faith that God requires for us to be accepted by Him and all the rest of the items of faith and practice. Thus many divisions are produced over trivial issues that should not have been issues at all. I was all too familiar with that from my background.
But if keeping the oneness means receiving believers with a wide variety of concepts and practices, then how can they remain in harmony? How can they deal with all the differences and the inevitable offences? There is only one way. The way is to put our self to death on the cross. There is absolutely no other way for Christians to remain in a practical and close oneness apart from each of them taking the cross. I may be able to get along with some who have similar backgrounds, dispositions and concepts but what about all the rest of God's children? Some of them are sure to bother me. How can I be one with them in serving the Lord when our ways of doing things, views and preferences clash so often? Many times I bother the ones I am serving with and many times they bother me. Perhaps I am too slow, perhaps another is too fast; in any case it is hard for us to go the same speed. The only way is for each of us to put ourselves aside and take the cross.
It seems to me that this is, in fact, both the biggest problem and the biggest blessing of exercising to keep the oneness. We have no way to remain in ourselves, or if we do, it soon becomes obvious because we become a problem to everyone else. Thus the Lord's transformation work on us can proceed much more quickly and thoroughly than if we are less closely related to other believers that, naturally speaking, we would never choose to be with. We may be able, if we guard our independence, to be in the body life without being blent with other saints but if we allow the Lord to deal with us through all the situations that arise, then we will grow into His likeness more and more.