Remember that John's epistle is written to church members. Therefore, he frames matters in absolute terms, offering no middle ground regarding sin and one's relationships with God and fellow man. It must be this way because this is our one and only opportunity for salvation, and sin was what cut us off from God in the first place, causing us to need salvation. We do not want to fall into that position again. Sin is serious business!
Regarding our moral and spiritual conduct, we must recognize that there is no twilight zone, especially in our relationship with God. A Christian cannot muddle around morally or spiritually, thinking that sin is a rather minor affair. It cost Jesus His life! In this relationship, which is in reality preparation for a marriage, love and loyalty are extremely important.
John spells matters out as either light or darkness, love or hatred, all absolutes. Where love is absent, hatred rules in darkness. Where love prevails, there is light. Through the word "darkness," John is disclosing that, because of the sin or hatred, a lack of love for a brother, the relationship with God declines. Notice in verse 11 that the sin John mentions is against a brother, meaning a fellow church member. Hatred is not a trifling matter! Later, in I John 3:15, John says that one who hates his brother is a murderer. What is the result? A relationship is broken, and communication with the brother ends.
Even more serious, we find that the sin also involves one's relationship with God because the effect of that sin is a measure of spiritual blindness. The hater grows insensitive to or hardened against spiritual truth.
Paul reinforces what John teaches, writing in Hebrews 3:12-13, "Beware brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; but exhort one another daily, while it is called 'Today,' lest any of you be hardened through the deceitfulness of sin." He warns that sin has a deceptive quality. It promises so much even before it actually becomes an act of conduct, but it delivers far short of its promise. Its truly sneaky aspect is its powerful tendency to lure us into further sin, enslaving us and hardening our minds against righteousness. In other words, it shares characteristics with drugs in that it is addictive or enslaving, destroying one's well-being.
Herein lies the cause of the apostle John's concern in I John 2. God is the source of spiritual truth (light), and we are sanctified as His children and to His service by it because we believe it. However, under the sin of hating, communication with God begins to break down, and consequently, the sinner puts himself in peril of falling completely away. Notice in I John 2:13-14, John mentions that the fathers - those in the congregation older in the faith - have known the Father. He appeals to them to exercise their longstanding, mature leadership within the congregation in a right manner.
The word "known" ties John's thoughts directly with Jesus' words in John 17:3. Knowing God, having an intimate relationship with Him, is the key to living a life - called "eternal life" - which will be acceptable for living in the Kingdom of God. Hating a brother actually cuts the sinner off from the Source of the gifts and strengths necessary to live that quality of life. In other words, the sinner is not properly using what God has already given him and is showing disloyalty both to God and to another member of the Family.
Beginning in verse 15, John pens three of the more notable verses in his writings. When considered in context, they should be scary stuff for a Christian. Why does he command us not to love the world? Because the sinner's conduct exhibited in his hatred of his brother reveals the source of communication prompting his sin! John exposes the communication to which the hater is responding.
Under no circumstance would God ever communicate the sin of hatred toward a brother. Besides, James confirms that God tempts no one (James 1:13). John is warning that the person's affections are drawing him away from God and toward the world, and he had better do something about it before he slips completely back into the world.
This also connects to John 1:5. "And the light shines in the darkness, and the darkness did not comprehend it." Darkness symbolizes the spiritual blindness of Satan's unconverted world. In the book of Revelation, this blindness is represented by Babylon the Great. Satan's world simply does not get it, that is, spiritual truth. Because it cannot grasp God's truths, the only spirituality the world can ultimately communicate is inducement to sin, which it does insistently and attractively.
This leads us back to God's illustration regarding Adam, Eve, and Satan. Satan is the god of this world (II Corinthians 4:4), and thus its spiritual leader and governing principle. He persuaded Adam and Eve to sin. So the only way we can come out of the world is to reverse the process that placed us in the world in the first place: to stop sinning. One can phrase it more positively as to yield to God's will rather than Satan's or to God's communication rather than this world's.
We could never leave the world on our own. God must mercifully deliver us by calling us. We do not understand the mechanics of what He actually does in our minds, but in calling us, He miraculously does something to begin leading us to think of matters in relation to God with a clarity of understanding and intensity that we never before experienced. It is almost as if we suddenly understood a foreign language.