It's because we're so bad at loving each other. It's because if people see the real love of Christ at work amongst his people, they will want to know what makes them like that. But if they see a bunch of quarrelling, self-centred pigs who act like they hate each other, then they won't even hear our message, let alone believe it. Because love is at the heart of the gospel message itself. And we ought to lay down our lives for our brothers.
Love is the flip side of faith.
But the faith that saves is never alone. That is, true saving faith will always produce works of love. Anyone who does not love remains in death. This love is very practical down to earth love. Dear children, let us not love with words or tongue but with actions and in truth.