Ray Ortland (quoting John Newton):
If you account him [your opponent] a believer, though greatly mistaken in the subject of debate between you, the words of David to Joab concerning Absalom are very applicable: “Deal gently with him for my sake.” The Lord loves him and bears with him; therefore you must not despise him or treat him harshly. The Lord bears with you likewise, and expects that you should show tenderness to others from a sense of the much forgiveness you need yourself. In a little while you will meet in heaven. He will then be dearer to you than the nearest friend you have upon earth is to you now. Anticipate that period in your thoughts. And though you may find it necessary to oppose his errors, view him personally as a kindred soul, with whom you are to be happy in Christ forever.