CLAIM: John writes, “Everyone who hates his brother is a murderer; and you know that no murderer has eternal life abiding in him” (1 Jn. 3:15). Are murderers not forgiven by the blood of Christ?
RESPONSE: The rest of the Bible categorically affirms that Jesus’ blood pays for all sin, including the sin of murder. The apostle Paul was a murderer who killed Christians (Acts 8:1; 22:19-20; 26:9-11), and he was forgiven. David was a murderer, killing Uriah, and he was forgiven as well (Ps. 32:1-2). Peter wrote that believers should not “suffer as a murder” (1 Pet. 4:15). In fact, the most evil and unjust murder that ever occurred on Earth was the murder of the son of God. Yet during his torture and murder, Jesus exclaimed, “Father, forgive them; for they do not know what they are doing” (Lk. 23:34). If these men could be forgiven for murdering the Son of God, then surely all sins can be forgiven.
John is equating hating our brother with murdering him. Therefore, if we are to take this verse at face value, then we would need to claim that anyone who hates his brother cannot have eternal life (cf. Mt. 5:21-22). Stott accepts this quite candidly: “He is rather stating as a general principle that to take life is to forfeit life and that no murderer has eternal life in him as a present and permanent possession. If this is so, and John accepts it as axiomatic, then clearly anyone who hates his brother does not possess eternal life either, because to hate is to be a murderer.” We find this to be practically untenable. If true, then we have never met an authentic Christian!
John most likely still has the false teachers in view. As Jesus said, “You are of your father the devil, and you want to do the desires of your father. He was a murderer from the beginning, and does not stand in the truth because there is no truth in him. Whenever he speaks a lie, he speaks from his own nature, for he is a liar and the father of lies” (Jn. 8:44).
One way to take this passage is that of knowing or recognizing a true believer. On this view, hatred for the Body of Christ is a sign that a person is not a true believer in Christ. This passage is given from the perspective of how we “know” if someone has eternal life.
Another way of taking this passage is to refer to our spiritual growth. John doesn’t write that the “murderer” does not have eternal life. He writes that he does not have eternal life abiding in him. This term “abiding” refers to our relational connection to Jesus, who is our eternal life (1 Jn. 5:20). Jesus taught us to “abide in him” so that he would “abide in us” (Jn. 15:4). This doesn’t mean that we gain and lose our salvation every time we draw near to God or forget about him. It means that we can have the present experience of sanctification as we abide in him.
 John R. W. Stott, The Letters of John: An Introduction and Commentary, vol. 19, Tyndale New Testament Commentaries (Downers Grove, IL: InterVarsity Press, 1988), 144.