Because of his encounter with the incarnate Son of God, John was compelled to broadcast this wonderful One to us and all who would hear:
That which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ.
And these things we write to you that your joy may be full.
The apostle makes the point that joy and fellowship are inextricably linked. God is the source of joy. The God/man is the means of appropriating that joy through our relationship to Him and then with His people.
As believers each of us has been baptized into the body of Christ. The body is vital connection and interdependence with coordinated work upon command from the head (Christ). While there is a common mission for the church there is also a common divine objective for each member of the body – the unity of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ – our joy!
Being conformed to Christ’s image is not something that is done alone. The mind of Christ and the law of Christ require investment with regard to others. Each of us plays an integral role in the spiritual growth (the joy of becoming like Christ) of the other. Our lasting joy in the Lord is proportionate to our maturity in the Lord and love/fellowship with His people.
This is why the apostle Paul told the Corinthian believers that they were fellow workers for your joy. Fellowship is what the apostle John did – the blessing he received from God he shared with those around him. What has been entrusted to you (God’s blessings) is for the express purpose of contributing to the joy of others.