I. The form of the announcement in the fifth verse is very peculiar: "This then is the message which we have heard of Him, and declare unto you." It is not a discovery which we make concerning God. It is an authentic and authoritative communication to us from Himself. The message is twofold. First, positively, "God is light"; next, negatively, "in Him is no darkness at all." (1) Positively, "God is light." Light is clear, transparent, translucent, patent, and open, always and everywhere, as far as its influence extends. It comes in contact with all things; it is itself affected by nothing. Thus "God is light," in His character perfectly open and perfectly inviolable. (2) Negatively, "in Him is no darkness." The light shineth in darkness, and "in Him is no darkness at all."
II. "If we say that we have fellowship with Him and walk in darkness, we lie, and do not the truth." The thing itself is impossible, for light hath no fellowship with darkness.
III. From the solemn message in the fifth verse and the faithful warning in the sixth the gracious assurance in the seventh fitly follows: "We have fellowship one with another," God with us and we with Him. It is our joint fellowship with God, and His with us, that alone is to the purpose here.
R. S. Candlish, Lectures on First John,p. 37.
Reference: 1 John 1:6. Spurgeon, Morning by Morning,p. 328.