Here’s how you know you’ve purified your heart with the gospel. You love other Christians without deceit, without hypocrisy, without envy, and without slander of any kind. That’s how you know. Let me put it a couple of ways. The reason love is the acid test of whether or not you believe the gospel is it is very possible to have both doctrinal purity and moral scrupulosity for other motivations and out of other forces besides the gospel.
It’s quite possible to be moral out of tradition, out of nostalgia, out of loyalty to your family, out of temperament, out of fastidiousness of conscience. There are all kinds of ways in which you could look at a person who’s very moral, and a person could say, ‘Well that proves that person is a Christian. That person really understands the message of Christianity.’ What Peter is saying here, and what the Bible says is no. A loving spirit is a far better acid test of whether you understand the gospel than moral scrupulosity.
– Tim Keller