The first three chapters of the Book of Ephesians are essential Church doctrine. The final three chapters of the Book of Ephesians are application for the life of the believer in essential Church doctrine.
Most of Paul’s epistles, (letters,) follow this format. As pastor Chuck Smith has said, it is good that Paul writes his letters in this format because it is always the case you must learn to sit and listen before you learn to walk. In the life of a newborn, it is always true they must learn to sit up and take instruction before they ever attempt to stand up and to walk. Paul follows this lead when speaking to those ‘newborn babes’ in the Church, (which we all once were – and some are now.)
The first thing Paul advocates for the Church is unity.
In speaking of unity, which only makes sense since we are speaking of the Body of Christ – and the Body of Christ is inseparable – Paul reminds the Church there is ONLY ONE of each of the essential doctrines which comprise and define the Church as being the Church.
Since there is only ONE body, and since there is only ONE Spirit – and since this is the source of our calling – it only stands to reason we would all worship ONE Lord, by ONE faith, which would proceed from ONE baptism into ONE God and Father of us all.
As Paul has written previously, all those who have placed their faith in Jesus Christ for salvation have been born again in Jesus Christ, and are all children of God and joint heirs with Christ whether a Jewish believer or a Gentile believer. Though the path to Christ may have been divergent, arrival IN Christ is convergent in every way.
(Jew and Gentile alike are baptized into Christ in exactly the same way, as Jesus Himself specified. Note also: Jew and Gentile alike are born again by placing their faith in Jesus Christ in exactly the same way, and all MUST BE born again regardless of Spiritual background or upbringing.)
The grace of God is the glue of the Church. All come to faith by the grace of God, and none come to faith in Christ apart from the grace of God.
So, apart from the flesh, how can there be disharmony or disunity in the Body of Christ?
The correct answer is their cannot be, and disharmony and disunity in the Body of Christ is ALWAYS a sign of carnality, whether in great degree or small.
Yet, when it comes to His Body, because it IS His body, He chooses to distribute gifts to His body as He sees fit. And there are many different Spiritual gifts distributed to His Body which allow the Body to function properly. This should be no surprise, and it must not be cause for jealousy or covetousness or dissent.
In fact, each part of the Body of Christ has received at least one Spiritual gift from Christ, and all the gifts are to function in co-dependency upon each other.
Paul immediately addresses exactly how this is to function when in proper order. The pastor-teacher is to inform (equip) the unified yet distinct parts of the Body about the doctrine of Christ which they are to operate under the authority of.
Supernaturally, it is the Body parts which are being equipped to accomplish the work of Christ, and it is the work of the pastor-teacher to inform the parts of the Body how they are to function in accomplishing His work. Nothing more and nothing less.
When every part of the Body of Christ contributes their share under the authority of Christ, the Church bears no resemblance to anything of this world – and this is exactly the way God intends it to be.