Francis Schaeffer proposed two simple (but profound) ways we Christians can display a powerful witness to the world:
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 judgements which these verses indicate: that we are not Christians, and that Christ was not sent by the Father.”
~ Francis A. Schaeffer, “The Mark of the Christian,”
in The Church at the End of the Twentieth Century, pages 143–146.