This is possibly the last apostolic message to the whole Church. It is complementary to the Gospel of John. Its subject is fellowship with God, into which believers are introduced through their union with Christ.
The whole fact of the mission of our Lord is declared to be a manifestation of eternal life. Concerning this John wrote, ‘We have heard,” “we have seen,” “we beheld,” “our hands handled.” The purpose of the manifestation was to bring men into fellowship with God. Through the manifestation of eternal life, and our reception of it by faith, we have fellowship with the Father. This means fellowship in Light, Love, and Life.
The first great message of the “word of life” to men is that “God is light.” The place of fellowship therefore is that of walking in the light of God. In God there is no darkness, neither can there be. If, then, “men love darkness rather than the light,” they are excluded from the fellowship of God.
Because of perpetual imperfection even in our most holy things there is need of a constant cleansing, which is provided in the ‘blood of Jesus His Son.” Light makes sin known. The sins of the past are forgiven, and the soul is cleansed from all unrighteousness.