The Epistle of John has a peculiar character. It is eternal life manifested in Jesus, and imparted to us–the life which was with the Father, and which is in the Son. It is in this life that believers enjoy the communion of the Father, that they are in relationship with the Father by the Spirit of adoption, and that they have fellowship with the Father and the Son. God’s own character is that which tests it; because it proceeds from Himself.
The first chapter establishes these two latter points: namely, communion with the Father and the Son, and that this communion must be according to the essential character of God. The name of Father is that which gives character to the second chapter. Afterwards it is that which God is, which tests the reality of imparted life. ...