He now returns to that, which he ever contemplates as the ground of the whole Christian life and of salvation, the ground of the whole church and of all its divine inward experiences, since upon this depends all and with this is given all, -- the testimony respecting the Son of God, whom the Father has sent as the Saviour of the world. Of this he bears testimony, with the confident assurance of an eye-witness: "And we have seen and do testify, that the Father sent the Son to be the Saviour of the world." But with those who had been so long acquainted with Christianity, he needed not to appeal merely to his own sight and experience. They were not to be dependent upon his personal testimony. The fact, to which he bore witness, must long since have fully attested itself, in their own conscious experience of fellowship with God attained thereby. But he would, again and again, impress it upon their hearts, that firm adherence to this fact must ever be the ground of all true fellowship with God. For faith he then substitutes confession; since faith must approve itself by an open confession of the Son of God, without fear or shame, in opposition to the world which ignores him and hates his followers. "Whosoever shall confess that Jesus is the Son of God, God dwelleth in him, and he in God." Assuming in christians this fellowship with God, which is the fruit of true adherence to faith in Jesus as the Son of God, he speaks not merely from his own personal experience, but as if uttering the experience of all; "And we have known and believed the love that God hath to us. God is love; and he that dwelleth in love, dwelleth in God, and God in him." The Apostle recognizes a reciprocal relation between knowledge and faith. The divine fact, which is the object of faith, must be in a certain manner known in order to be believed. But it is by receiving through faith this divine fact into the heart and making it properly our own, that we first become truly acquainted, in the experiences of the inner life, with the object of faith; and therefrom develops itself the true knowledge of that object, not as something external to the spirit, but as being through this inward experience a part of itself. In the spirit enlightened by faith, knowledge is developed; and faith, through the knowledge derived from this inward experience, receives in turn a higher import. We believe in the love of God toward us, because we know it by this inward experience. This is the kind of knowledge here meant. But in thus knowing God's love for us, we come to know God himself; and in that way in which he can most perfectly be known, for his nature is love.
Abiding in love is represented by the Apostle: as the condition and the token of abiding in fellowship with God. By love he doubtless means, as the connection shows, primarily the love of God as revealing itself in Christ the Saviour of the world, and making itself felt in the hearts of believers; and as then, by the light of faith becoming an object of knowledge. They attain to a conscious knowledge of that which is their life-element. But their hearts cannot be filled with this overflowing love of God, without producing in return that love to God, and to the brethren, which has its root therein.