God is love

God is love: that is, love is not a human behavior, sentiment, or deed, but it is God who is love. What love is can be known only by one who knows God; the reverse is not true, that one would first know what love is—that is, from nature—and therefore also know what God is. But nobody knows God except one to whom God reveals himself. Thus nobody knows what love is except through God’s self-revelation. Love is therefore God’s revelation. God’s revelation, however, is Jesus Christ.

Dietrich Bonhoeffer, God’s Love and the Disintegration of the World, p. 334