In 1 John 4:7-12, the Apostle of Love gives three reasons why Christians love each other. First, they love because of who God is (vv. 7-8). Second, they love because of what God has done (vv. 9-11). And third, we love because of what God is doing (vv. 12).
First, Christians love because of who God is. Who is he? He is the source of love. “Dear friends, let us love one another, because love is from God…” The Greek here is lyrical. The King James and at least one modern version try to capture it by translating, “Beloved, let us love…” Greek is Ἀγαπητοί, ἀγαπῶμεν. “Beloved, love…” Why? Because love is from God. When Christians love one another, the source of their love is God himself. And as his love is transmitted through their emotions, minds, and wills, they experience God and are changed.
All genuine love comes from God. This means that a parent’s love for a child comes from God, even if that parent doesn’t realize or acknowledge it. The love that causes a soldier to sacrifice himself to save his brothers and sisters comes from God, though he may not know it. In some cases, the people who love do not know where that love originated, but in our case it is different. We can knowingly enter into the love God has for others, make ourselves its conduit, and so experience God’s life flowing through us.
But John goes beyond saying that love come from God. He makes the daring statement that God is love. There are some things to keep in mind. First, saying that “God is love” is a very different thing from saying that love is God. What people call love is often not the self-giving love expressed in Christ but the hungry, grasping, desire expressed by needy people. Hollywood elevates that desire to divine status and makes a fortune. But if we do the same, we will only make a mess.
God is love. This is one of four explicit statements about the nature of God in the Bible. Jesus says that God is Spirit (John 4), John says that God is light (1 John 1), and the author of Hebrews (12), quoting Deuteronomy 4, says that God is a consuming fire. Don’t get the idea that because God is love, he is a softy. That, because he is love, we can sin without consequence. For the Divine Spirit who is love is also light and fire.
Because God is light, he exposes our sins. Because he is fire, he consumes our sins. But because he is love, he has found a way to expose and consume them without destroying us. That way – and it is a costly way – is the cross of Christ. It is in the cross that the God who is light shines most brilliantly. In the cross, the God who is fire burns most intensely. And in the cross, the God who is love gives most passionately.
 See John Stott, Tyndale New Testament Commentaries: The Epistles of John. pp. 160-161