Here’s what Tim Keller writes in an extended callout in Center Church: Doing Balanced, Gospel-Centered Ministry in Your City (Grand Rapids: Zondervan, 2012), 376–80:

GOSPEL POLEMICS

All Christian movements must be based on commonly held biblical truths, and yet they must be characterized by trust and a willingness to unite around central truths and accept differences on secondary matters that—in the view of ministry partners—do not negate our common belief in the biblical gospel. On the one hand, we must realize that if we are going to maintain a healthy movement over time, we have to engage in direct discussion about any doctrinal errors we perceive. On the other hand, we must engage in such a way that we show great respect for the other party and aim to persuade them, not just punish them.

How can this be done? I suggest the following principles for “polemics”—contending over doctrine—that is seasoned in tone and strategy by the gospel itself. As I’ve read a number of respected Christian authors over the years, I have distilled a few “rules of engagement” that I believe can keep us from either avoiding polemics or engaging in it in a spiritually destructive way.

1. Take full responsibility for even unwitting misrepresentation of others’ views. In our Internet age, we are quick to dash off a response because we think Mr. A promotes view X. And when someone points out that Mr. A didn’t mean X because over here he said Y, we simply apologize—or maybe we don’t even do that. Great care should be taken to be sure you really know what Mr. A believes and promotes before you publish. This leads to a related rule.

2. Never attribute an opinion to your opponents that they themselves do not own. Nineteenth-century Princeton theologian Archibald Alexander stated that we must not argue in such a way that it hardens opponents in their views. “Attribute to an antagonist no opinion he does not own, though it be a necessary consequence.” In other words, even if you believe that Mr. A’s belief X could or will lead others who hold that position to belief Y, do not accuse Mr. A of holding to belief Y himself if he disowns it. You may consider him inconsistent, but this is not the same as implying or insisting that he actually holds belief Y when he does not. A similar move happens when we imply or argue that if Mr. A quotes a particular author favorably at any point, then Mr. A must hold to all the views held by the author. If we, through guilt by association, hint or insist that Mr. A must hold other beliefs of that particular author, then we are not only alienating him or her; we are also misrepresenting our opponent.

3. Take your opponents’ views in their entirety, not selectively. A host of Christian doctrines have an “on the one hand/on the other hand” dimension about them—and without both emphases we can fall into heresy. What if we find Mr. A making what appears to be an unqualified statement that sounds very unbalanced? If that is all Mr. A ever said about the subject, it would be right to conclude something about his position. But what if Mr. A has been speaking or writing these statements to an audience that already believed certain things, and therefore he was assuming those points of doctrine without stating them? At minimum, we must realize that Mr. A simply can’t say everything he believes about a subject every time he speaks. We should not pull out certain statements by Mr. A while overlooking or actually concealing explanations, qualifications, or balancing statements he may have made elsewhere.

4. Represent and engage your opponents’ position in its very strongest form, not in a weak “straw man” form. This may be the most comprehensive rule of all in polemics, because, if you adhere to it, most of the other policies and principles will follow. Do all the work necessary until you can articulate the views of your opponent with such strength and clarity that he or she could say, “I couldn’t have said it better myself.” Then, and only then, will your polemics have integrity and actually have the possibility of being persuasive—which leads to our next point.

5. Seek to persuade, not antagonize—but watch your motives! John Calvin was a Reformer in Geneva, Switzerland. His comrade in this work was William Farel, who was outspoken and hotheaded by temperament. At one point, Calvin wrote Farel a letter in which he urged Farel to do more to “accommodate people”—i.e., to seek to persuade them, to win them over. Calvin then distinguished two very different motivations for seeking to be winsome and persuasive: “There are, as you know, two kinds of popularity: the one, when we seek favor from motives of ambition and the desire of pleasing; the other, when, by fairness and moderation, we gain their esteem so as to make them teachable by us.”

The Farels of the world believe any effort to be judicious and prudent is a cowardly sellout. But Calvin wisely recognized that his friend’s constant, intemperate denunciations often stemmed not from a selfless courage, but rather from the opposite—pride. Writing to Pierre Viret about Farel, Calvin said, “He cannot bear with patience those who do not comply with his wishes.”

In short, it is possible to seek to be winsome and persuasive out of self-centeredness rather than God-centeredness. We may be winsome in an attempt to be popular. It is just as possible to be bold and strongly polemical out of self-centeredness rather than God-centeredness. And therefore, looking very closely at our motives, we must take care that our polemics do not unnecessarily harden and antagonize our opponents. We should seek to win them, as Paul did Peter, not to be rid of them.

6. Remember the gospel and stick to criticizing the theology—because only God sees the heart. Much criticism today is filled with scorn, mockery, and sarcasm rather than marked by careful exegesis and reflection. Such an approach is not persuasive. No one has written more eloquently about this rule than John Newton in his well-known “Letter on Controversy.”

Newton states that before you write a single word against your opponent “and during the whole time you are preparing your answer, you may commend him by earnest prayer to the Lord’s teaching and blessing.” This practice will stir up love for him, and “such a disposition will have a good influence upon every page you write.” Later in the letter, Newton writes:

What will it profit a man if he gain his cause and silence his adversary, if, at the same time, he loses that humble, tender frame of spirit in which the Lord delights, and to which the promise of his presence is made? … Be upon your guard against admitting anything personal into the debate. If you think you have been ill treated, you will have an opportunity of showing that you are a disciple of Jesus, who “when he was reviled, reviled not again; when he suffered, he threatened not.”

Newton also reminds us that it is a great danger to “be content with showing your wit and gaining the laugh on your side,” to make your opponent look evil and ridiculous instead of engaging their views with “the compassion due to the souls of men.”

The fourth principle above is especially important. Compare what Keller says earlier in the book:

• The first step in active contextualization is to understand and, as much as possible, identify with your listeners, the people you are seeking to reach. This begins with a diligent (and never-ending) effort to become as fluent in their social, linguistic, and cultural reality as possible. It involves learning to express people’s hopes, objections, fears, and beliefs so well that they feel as though they could not express them better themselves. (p. 120, emphasis added)
• Directly address and welcome nonbelievers. Talk regularly to “those of you who aren’t sure you believe this or who aren’t sure just what you believe.” Give several asides, even trying to express the language of their hearts. Articulate their objections to Christian doctrine and life better than they can do it themselves. Express sincere sympathy for their difficulties, even as you challenge them directly for their selfishness and unbelief. (p. 308, emphasis added)

Related: “How Should You Relate to Fellow Christians When Your Consciences Disagree about Disputable Matters?”, ch. 5 in Conscience