“A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. By this all people will know that you are my disciples, if you have love for one another.” John 13:34-35
Three things here. One, the command of Christ, that we love one another. Two, the example of Christ, that we are to love one another as he loved us. Three, the promise of Christ, that all kinds of people will see we are real disciples of Christ, when we love one another his way.
Francis Schaeffer proposed two powerful things we can do, to display observable love for one another in response to these verses and also John 17:23:
One, “When I have failed to love my Christian brother, I go to him and say, ‘I’m sorry.’ That is first. It may seem a letdown — that the first thing we speak of should be so simple. But if you think it is easy, you have never tried to practice it. . . .”
Two, “There must also be open forgiveness. And though it’s hard to say ‘I’m sorry,’ it’s even harder to forgive. The Bible, however, makes plain that the world must observe a forgiving spirit in the midst of God’s people. . . .”
“[Does the world] observe that we say ‘I’m sorry,’ and do they observe a forgiving heart? Let me repeat: Our love will not be perfect, but it must be substantial enough for the world to be able to observe it, or it does not fit into the structure of John 13 and 17. And if the world does not observe this among true Christians, the world has a right to make the two awful judgments which these verses indicate: that we are not Christians, and that Christ was not sent by the Father.”
Francis Schaeffer, “The Mark of the Christian,” in The Church at the End of the Twentieth Century (Downers Grove, 1970), pages 143-146.
The primary barrier to the advance of the gospel in our generation is not out in the world. The primary barrier is us Christians who do not practice Christianity as it was defined originally by Christ. We have our Christianity, with layers of historical accretions separating us from the real thing. Christ had his Christianity, and we need to peel away our layers and go back and recover Christ’s Christianity. In other words, what is needed in our time is nothing less than the re-Christianization of us Christians. Isn’t it obvious that we who say we are Christians should understand Christianity? Its greatest mark is our observable love for one another. Christ himself said so.