Schaeffer says our love must be observable, something others can see. Observable love often requires saying sorry and asking for forgiveness—with a spouse, a friend, a child, a parent, or another person or group we’ve wronged. This is simple, but it won’t be easy. In my experience, it takes great strength of character to say, “I’m sorry. I was wrong. Will you forgive me?”

Editors’ note: Taking the advice of C. S. Lewis, we want to help our readers “keep the clean sea breeze of the centuries blowing through our minds,” which, as he argued, “can be done only by reading old books.” To that end, our Rediscovering Forgotten Classics series surveys some forgotten Christian classics that remain relevant and serve the church today.

I tend to tune out social media controversies and negative online comments. It’s generally a good course of action given the storms of shock and outrage about nearly everything on any given day. Even attempts at good-faith responses sometimes fan the flames.

Avoiding such storms works well because of the distance the internet provides. But when Henry, a real-life friend of mine, objected on social media to something I was personally involved with, it raised a different set of questions. Since the critique was on social media, should I respond there? Should I give a long, nuanced reply, sure to be read by few? Should I say something punchy, sure to get everyone’s attention? Should I ignore it? As Christians, how can we learn to disagree well, especially with other Christians?

In 1970, Francis Schaeffer, one of the most astute apologists of the 20th century, published The Mark of the Christian. I first read the book about 50 years ago, and it continues to shape how I think about encounters like the one with my friend. It’s a brief book; you can read it in about an hour. Yet it may carry more weight today than at any time in the last half-century because it reminds us of the importance of loving our neighbor and being able to disagree well—vital skills in an increasingly polarized age.

Two Passages in John

The Mark of the Christian is Schaeffer’s meditation on two passages in John’s Gospel. He begins with John 13:34–35: “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.”

Schaeffer marvels at Jesus’s words:

In the midst of the world, in the midst of our present dying culture, Jesus is giving a right to the world. Upon his authority he gives the world the right to judge whether you and I are born-again Christians on the basis of our observable love toward all Christians. . . .

In other words, if people come up to us and cast in our teeth the judgment that we are not Christians because we have not shown love toward other Christians, we must understand that they are only exercising a prerogative which Jesus gave them. And we must not get angry. . . . We must go home, get on our knees and ask God whether or not they are right. (22–23)

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