One of the most eloquent admonitions I have ever encountered along these lines is in Bishop Burnet’s preface to the classic work The Life of God in the Soul of Man, written by Henry Scougal in the latter part of the seventeenth century. Here is what Burnet wrote:

“There is scarce a more unaccountable thing to be imagined, than to see a company of men professing a religion, one great and main precept whereof is mutual love, forbearance, gentleness of spirit, and compassion to all sorts of persons, and agreeing in all the essential parts of its doctrine, and differing only in some less material and more disputable things, yet maintaining those differences with zeal so disproportional to the value of them, and prosecuting all that disagree from them with all possible violence; or if they want means to use outward force, with all bitterness of spirit. They must needs astonish every impartial beholder, and raise great prejudices against such persons’ religion, as made up of contradictions; professing love, but breaking out in all the acts of hatred.”

Surprised by the Power of the Spirit, Jack Deere (Grand Rapids: Zondervan Publishing House, 1993), pp. 176, 177.