The simple statement “God is love” is very complex. What does John mean by this? (4:16b). Love is a “defining characteristic of God” (Jobes, 1, 2, & 3 John, 190). If the father is love, then so too is the son. Those who have been born of God ought to have this same characteristic as their heavenly father.
Raymond Brown points out saying “God is love” is not the same as saying “God loves” (Brown, Epistles of John, 515). Since God is love, everything he does is an expression of his love. In this context, John mentions the coming Day of Judgment. Even rendering judgment and punishing those who remain in their sin is an act of love because God can only act in accordance to his loving character.
By abiding him God, his love has been perfected (4:17a). This is another example of John’s subtle use of grammar. He chooses the perfect passive form of τελειόω to emphasize God’s love has already been made perfect in the past and it remains perfect at the time he is writing.
By perfected (ESV), John means something like “brought to completion” or “reaches the intended goal.” This is not at all like the human emotion of love, which ebbs and wanes over the years. God’s love is not an emotional response; it is a real and concrete action based on his loving character to sacrifice everything on behalf of those who do not even recognize his existence or authority.
Because God’s love has been perfected in us, we will have confidence on the Day of Judgment (4:17b-19). The Day of Judgment is eschatological, looking forward to a time when the believer will stand before Jesus as a judge. This sounds as if one is judged on whether they are going to “go to heaven” or now, but that is not what John says. All he says here is when the one who has really grown mature in love or their brother and sister, they can have nothing to be ashamed about standing before the judge. They are “right with God” because God has provided his son as an atoning sacrifice (1 John 4:7-10) and they know that they have this relationship with God because they (in fact) love their brother and sister.
There is no fear of punishment on that day: perfect love casts out fear. This verse is usually taken out of context. Unfortunately there are many people who do have genuine fear because of they have experienced terrible things at the hands of people who claimed to be Christians. This may be judgement because of sin, but too many people have been abused by people claiming to have spiritual authority.
If the church was really doing the love of God as demonstrated in the gracious sacrifice of Jesus on the cross as an atoning sacrifice, then the church would be far more attractive to those who remain in the world. As John says in 4:20-21, one cannot claim to be a Christian if they hate their fellow Christian; how much more if they hate the unsaved?
The only reason we can love others are demonstrate that we abide in God is that God has loved us first and sent his some as savior.
One cannot claim to love God and hate a brother or sister in Christ (4:20-21). Once again John demands concrete action in the real world as evidence for one’s claim to love God. The person who claims to be a Christian and expresses hatred toward others is an impossibility for John.