John’s transition (v. 3) to the subject of knowing God may seem more abrupt than it really is. In ancient thought, the concept of “light” readily suggested the idea of “vision,” “perception,” or “knowledge.” It seems obvious that a life of fellowship with God in the light ought to lead to knowing Him. Of course in a sense all true Christians know God (John 17:3), but sometimes even genuine believers can be said not to know God or Christ (John 14:7–9).

fellowship naturally leads to knowing the One with whom that fellowship takes place. Even on the level of human experience this is true. If a father and son live apart, they will not know each other as well as if they lived together, even though their parent-child relationship continues to exist.

someone may profess a fellowship with God which his life shows he does not possess. John was not afraid to call this kind of claim what it really is: a lie

In such a person the truth is not a dynamic, controlling influence. He is seriously out of touch with spiritual reality.

It would be a mistake to equate the concept of being “in Him” as John uses it here with the Pauline concept of being “in Christ.” For Paul, the words “in Christ” describe a Christian’s permanent position in God’s Son with all its attendant privileges. With John, the kind of relationship pictured in the vine-branch imagery describes an experience that can be ruptured (John 15:6) with a resultant loss of fellowship and fruitfulness. Thus here in 1 John, the proof that a person is enjoying this kind of experience is to be found in a life modeled after that of Jesus in obedience to His Word. In short, 2:5–6 continues to talk about the believer’s fellowship with God.

John did not have in mind some new obligation which his readers had never heard. On the contrary the command foremost in his mind was an old one, which you have had since the beginning (cf. 2 John 5). No doubt John thought here especially of the command to love one another (cf. 1 John 2:9–11). He emphasized his point by adding that this old command is the message (logos, lit., “word”; cf. 1:5; 3:11) which you have heard (the majority of mss. add again “from the beginning”). Whatever innovations the readers might be confronting because of the doctrines of the antichrists, their real responsibility was to a commandment which they had heard from the very start of their Christian experience (cf. “heard” and “from the beginning” in 1:1; 2:24; 3:11).

John was warning his readers against a spiritual danger that is all too real (cf. 1:8, 10). And he was affirming that a Christian who can hate his fellow Christian has not genuinely escaped from the darkness of this present passing Age. To put it another way, he has much to learn about God and cannot legitimately claim an intimate knowledge of Christ. If he really knew Christ as he ought, he would love his brother.

Hatred is a kind of internal “stumbling block” which can lead to disastrous spiritual falls. But the calamities to which hatred leads are avoided by one who loves his brother.

Hatred is a kind of internal “stumbling block” which can lead to disastrous spiritual falls. But the calamities to which hatred leads are avoided by one who loves his brother.

This is not so, however, for one who hates his brother. Such a person walks around in the darkness and he does not know where he is going, because the darkness has blinded him (cf. v. 9). A Christian who harbors hatred for a fellow Christian has lost all real sense of direction. Like a man wandering aimlessly in the dark, he faces potentially grave dangers.