Ephesians 3:6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel:
The first Church were the Jew, they are the first partaker of the the promise of God. Therefore, the Gentile also were give the opportunity to be partakers of His promise through Christ Jesus.
We are members of the body of Christ and partakers of His promise through Christ Jesus. The Apostle and the Jew are first members. We give the privilege to be member to the body of Christ by accepting Jesus our personal Lord and Saviour and obey the doctrines of Christ Jesus.
We need to follow the doctrine Christ as it is written in the Bible. We are to add to the doctrine of Christ, neither should we remove from it. The gospel is the doctrine.
Ephesians 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
The Gospels bring about salvation. After receiving the gospel of Christ, we were seal with the Holy Spirit with Jesus promise us.
1 Corinthians 15:2 By which also ye are saved, if ye keep in memory what I preached unto you unless ye have believed in vain.
Those doctrine to obey. It not the gospel of the we raising our and in meeting. The doctrine is in the words of God and are to be followed as body of Christ.
Philippians 1:27 Only let your conversation be as it becometh the gospel of Christ: that whether I come and see you, or else be absent, I may hear of your affairs, that ye stand fast in one spirit, with one mind striving together for the faith of the gospel;
Just as is written in the above Scripture, we are to deal we our neighbour diligently in love and be modest in our dressing and characters
The doctrine of Christ is the doctrine of truth and salvation.