Borrowed from Tom Ascol, here are some large excerpts from a letter by John Newton to a friend preparing to engage in a public theological controversy:

Dear Friend,

As you are likely to be engaged in controversy, and your love of truth is joined with a natural warmth of temper, my friendship makes me solicitous on your behalf. You are of the strongest side; for truth is great, and must prevail; so that a person of abilities inferior to yours might take the field with a confidence of victory. I am not therefore anxious for the event of the battle; but I would have you more than a conqueror, and to triumph, not only over your adversary, but over yourself....For method's sake, I may reduce my advice to three heads, respecting your opponent, the public, and yourself.

CONSIDER YOUR OPPONENT

...If you account him a believer, though greatly mistaken in the subject of debate between you,... "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...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.

...But if you look upon him as an unconverted person, in a state of enmity against God and his grace, ... he is a more proper object of your compassion than of your anger. Alas! "He knows not what he does." But you know who has made you to differ. If God, in his sovereign pleasure, had so appointed, you might have been as he is now; and he, instead of you, might have been set for the defense of the gospel. You were both equally blind by nature. If you attend to this, you will not reproach or hate him, because the Lord has been pleased to open your eyes, and not his.

CONSIDER THE PUBLIC

First, such as differ from you in principle... Though you have your eye upon one person chiefly, there are many like-minded with him; and the same reasoning will hold, whether as to one or to a million.

There will be likewise many who pay too little regard to religion. ...These are very incompetent judges of doctrine; but they can form a tolerable judgment of a writer's spirit. They know that meekness, humility, and love are the characteristics of a Christian temper; ...They are quick-sighted to discern when we deviate from such a spirit, and avail themselves of it to justify their contempt of our arguments. ...If our zeal is embittered by expressions of anger, invective, or scorn, we may think we are doing service of the cause of truth, when in reality we shall only bring it into discredit. The weapons of our warfare, and which alone are powerful to break down the strongholds of error, are not carnal, but spiritual; arguments fairly drawn from Scripture and experience, and enforced by such a mild address, as may persuade our readers, that, whether we can convince them or not, we wish well to their souls, and contend only for the truth's sake; if we can satisfy them that we act upon these motives, our point is half gained; they will be more disposed to consider calmly what we offer; and if they should still dissent from our opinions, they will be constrained to approve our intentions.

[those who agree with you] ...Self-righteousness can feed upon doctrines as well as upon works; ...Controversies, for the most part, are so managed as to indulge rather than to repress his wrong disposition; and therefore, generally speaking, they are productive of little good. They provoke those whom they should convince, and puff up those whom they should edify.

CONSIDER YOURSELF

...And yet we find but very few writers of controversy who have not been manifestly hurt by it. Either they grow in a sense of their own importance, or imbibe an angry, contentious spirit, or they insensibly withdraw their attention from those things which are the food and immediate support of the life of faith, and spend their time and strength upon matters which are at most but of a secondary value. This shows, that if the service is honorable, it is dangerous. What will it profit a man if he gains his cause and silences 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." This is our pattern, thus we are to speak and write for God, "not rendering railing for railing, but contrariwise blessing; knowing that hereunto we are called." The wisdom that is from above is not only pure, but peaceable and gentle; and the want of these qualifications, like the dead fly in the pot of ointment, will spoil the savor and efficacy of our labors.

If we act in a wrong spirit, we shall bring little glory to God, do little good to our fellow creatures, and procure neither honor nor comfort to ourselves. If you can be content with showing your wit, and gaining the laugh on your side, you have an easy task; but I hope you have a far nobler aim, and that, sensible of the solemn importance of gospel truths, and the compassion due to the souls of men, you would rather be a means of removing prejudices in a single instance, than obtain the empty applause of thousands.