Keeping the unity of the Spirit requires first of all that we live in Spirit. Simply following any teaching outwardly, no matter how good and accurate it is, is in the principle of law keeping. It is the Spirit that gives life and it is only when we are in spirit that we can be truly one with others. Secondly, we need to avoid any kind of name or label that distinguishes us from other believers. We are simply believers in Christ who are enjoying the grace of His salvation. We are not bothered by the names others may use to denominate themselves. Nor do we try to convince them to be the same as ourselves in doctrine or practice. If the Lord has received them, then we receive them. The only things we would insist on are the basic beliefs in the Lord's person and work which distinguish believers in Christ from those who do not believe. Thirdly, we honour whatever work the Lord has done in other believers. The Lord's work in each one is unique which is one of the reasons we need one another's portions to adequately express the Lord.
In its practical application, the matter of keeping the oneness of the Spirit is a constant test to believers. A Christian cannot maintain the freshness of his relationship with the Lord in isolation; he needs fellowship. However, when we are with others, especially when we try to serve the Lord together, many things can spoil the sweetness of our fellowship. We all have the same Lord, but we each also have our own preferences, concepts, ways of doing things, etc. Not only so, we make mistakes and offend and misunderstand one another. If that weren't enough, our fallen nature is prone to pride, jealousy, rivalry, partiality, etc.
All who have received the Lord are already one in spirit. The Spirit of God entering into and giving life to our spirits has made us one both with the Lord (1 Cor. 6:17) and with one another. But the different concepts and opinions in our minds, our fickle and easily offended emotions, our stubborn wills, and our sinful flesh, all can disturb our peace and cause us to lose our oneness. In other words, in our spirits we are already one, but in our selves there can be many problems.
So how can we keep the oneness of the Spirit? There is only one way. Whenever issues arise, we need to find the Lord. The issue, offence, etc. is a chance for us to gain something of the Lord. None of us is 100% mature in the Lord but once we receive the Lord, He begins to work in our hearts to conform us to His own image. Aspect by aspect, He begins to work to gain each part of our heart. This is His work of transformation in us. If we can find the Lord in each situation, learning to deny ourselves and take the cross, then there will be two results. We will both be kept in the oneness of the Spirit and we will be constantly growing in the Lord.
The problem the Lord has with us is that most of the time we do not recognize what is still of our natural being. We don't know what in us is frustrating the Lord. So the Lord allows things to come up, even attacks of the enemy that sow discord and enmity among brothers, that expose what is in our hearts. Every natural and fallen element in our hearts is a weak point that gives the enemy an opportunity to attack. It is correct to say that the problems that arise are from the enemy but is also correct to say that the Lord allows them in His sovereignty. The issue for each of us is not who is right and who is wrong. In fact, the harder tests are when we really are right and are being misunderstood or wronged. Can we turn our hearts to the Lord and allow Him to fill our heart with His in that matter? This is how the Lord grows in us. This is how we can keep the oneness of the Spirit.