10 Whoever loves his brother [believer] abides (lives) in the Light, and in It or in him there is no occasion for stumbling or cause for error or sin.
11 But he who hates (detests, despises) his brother [in Christ] is in darkness and walking (living) in the dark; he is straying and does not perceive or know where he is going, because the darkness has blinded his eyes. (Read 1 John 2:3-11).
9 This verse brings us to the third false claim that the author denies. Whereas obedience to the new command leads to love among the Christian community, among the opponents who claim to "be in the light" there is hate. This hate for one's fellow believer shows that the light they follow is nothing but darkness.
How does John understand hate? His answer lies primarily in what one does. Hate is the absence of the deeds of love. To walk in the light is to love one's brother, and God's love will express itself in concrete actions. If these are missing, it is not because love can be neutral or can exist unexpressed. Love unexpressed is not love at all. When it is absent, hate is present.
In this instance, hate is the failure to deny oneself, the unwillingness to lay down one's life for a brother (Jn 15:13). On considers one's own plight first (1 Cor 13:5); disregards the robbed and afflicted (Lk 10:30-37); despises the little ones (Mt 18:10); withholds the cup pf cold water from the thirsty (Mt 25:43). Whenever a brother has need and one does not help him, then one has, in fact, hated his brother.
Does the word "brother" refer here to one's neighbor or to one who belongs to the community of faith? In this instance it probably refers to a member of the community of faith. It is not that John lacks concern for those outside the faith: rather, in this letter he has the community of believers in view. Moreover, if believers cannot love their fellow believers, it is doubtful that they can truly love their neighbors.
10 The author now gives us a positive test of living in the light. Unlike his opponents, his concern is with deeds, not claims. "Whoever loves," he says, is "in the light." Conversely, the one who does not live "in the light" will not manifest God's love.
11 Now the author picks up the concept of "darkness" from v.9 and gives it a final elaboration and conclusion. One who "hates his brother" is not simply "in the darkness" but is condemned to spend his life in darkness. Though he has eyes, he can see nothing. And the darkness so blinds his eyes that he has no idea "where he is going." Life is a search, but for him it is without direction. He never knows whether he is closer to or farther from his destination. The only certainty is that he is without hope of reaching it. So hate destroys any window for light from God. To live without loving one's brother means to deny oneself the presence of God and the reality of fellowship with the community of faith.
[NIV BIBLE COMMENTARY Volume 2: New Testament].
JESUS IS LORD.