One of my young friends has asked me how to "defend the truth without brutally maiming one's erring brothers." That's a good and worthwhile question. Sadly, answering is easier than doing. It is only by the Spirit of Christ that we are enabled to accomplish it. Here is how I would answer the question, therefore, in accordance with His Word, which is the very means by which His Spirit works.
Your brother is not your enemy, no matter what either one of you may think of the other. If he is your brother, than he belongs to you in Christ Jesus (and if he is not your brother, the Lord would call him to become your brother in Christ). You have one enemy, that is the devil, who is a liar and a murderer. If your brother has fallen into the snare of the devil, then you and your brother have a common enemy, and now you are given to aid your brother. Defend the truth, therefore, in order to thwart the power of the devil's lies over your brother. Contend for the faith, in order that your brother may have life in Christ instead of death.
The goal is not to win the argument, but to win your brother. Your aim is to be reconciled to him; not by any compromise of the truth, but by harmonious agreement in the truth. If it is the faith and the truth for which you are concerned, then it is not about you, but about Christ Jesus. Not as though Jesus needed your help, but because your brother does.
Listen carefully and compassionately to what your brother has to say. Be patient and considerate. If he is in error, you will not be able to help him if you do not hear him accurately. He may not be far from the Kingdom of God, to begin with, but you may push him further away if you are too quick to speak before you have listened. Such impatience and such a rush and hurry to correct your brother, more likely stems from a defensiveness of your own sinful weakness and uncertainty than from the conviction of faith and the confidence of truth.
Bear in mind that your own faculties of intelligence, knowledge and wisdom, are fallen and imperfect. It is not only your body and your heart that are tainted by your sin, but also your mind. Allow that your own understanding may need to be corrected. Or, while it may be true that your faith is quite rightly informed, it may also be the case that your confession of the faith needs to be ordered with greater clarity.
Do not hesitate to acknowledge your own errors when they are brought to light by the Word of God. Do not fail to apologize where you have spoken poorly, and to confess your sin where you have spoken falsely. What is more, do not fail to apologize where you have spoken the truth in a manner unbecoming of a Christian. Do not apologize for the truth, of course, but own the error for whatever in your words and actions has denied that very truth which you confess.
In humility, consider others to be better than yourself. Think more highly, even of your erring brother, than you think of yourself. Be more zealous for your brother's needs than your own, especially if you have been given a greater knowledge and better understanding of the truth than he has received. If you have been granted wisdom, thank God for His grace and mercy toward you, and recognize the privilege and responsibility that He has given you to confess the faith according to His Word.
Just as the Lord does and accomplishes everything by His Word, which alone endures forever, defend the truth by speaking His Word. Say the same thing that God the Father speaks to you by His Son. In thus confessing His Word, it is God who speaks through you, and it is the Spirit who works in your brother. Speak that most powerful Word in humility, because it is the Word of God, whereas you are a sinful man or woman; but speak it with confidence, nevertheless, precisely because it is the Word of God, even when spoken by sinners. You do not empower it with your eloquence, nor do you render it impotent by your stammering tongue. If you would contend for the faith, do so by no other means than by the confession of God's Word.
In speaking the Word of God, you speak the Truth. His Word is Spirit and Truth. Ultimately, His Word is Christ, the incarnate Son, the anointed One, the Savior of all men. Thus, in speaking the Word of God, speak Christ above all. Speak the Law, because Christ is the fulfillment of the Law. Speak the Gospel, because Christ desires all men to be saved and to come to the knowledge of the Truth. It is true that in speaking the Law, you do risk killing your brother; or, rather, it is the Lord who kills him, putting the old Adam to death. But in this you do no harm to your neighbor; for the Lord kills in order to make alive, He chastens and He heals. Speaking the Truth of His Word never does make things worse, although it may seem like it for the time being. Speaking the Truth of His Word is the only way to make anything better.
Speak the Truth of His Word — both painful and sweet, both deadly and life-giving, the Law and the Gospel — in season and out of season, but always in love. Speak to your brother in love, for love's sake, and not for your own vindication or pride or accomplishment or repuation. Speak the Word of Christ, who is Love incarnate. You are not really defending the truth, nor contending for the faith, if you speak for any other purpose than love. Certainly, the Word of Christ that you may yet confess shall accomplish the purpose for which He has spoken it, and your brother may thus benefit, in any case, by the grace of God. But as for what you are doing with your words and your contending, if you have not love, it is not of God that you are speaking. Yet, the love of Christ constrains you, and so, for the love of God, do speak.
Speak the Truth in love. Not only for love's sake, but let love itself be the very language that you speak. Not superficial or frivolous emotion, but the self-sacrificing love of God in Christ. That love alone melts hearts of stone and turns them from idolatry to serve the true and living God. This Love, incarnate in the Crucified One, speaks with gentleness, peace and forgiveness. That is how you are to speak, therefore, even to those who hate you and persecute you and say all manner of evil about you, for Jesus' sake.
Consider the example of our Lord, who, when He was reviled, did not revile in return. Instead, He entrusted Himself to the Father, who hands Him over to the Cross for our salvation. He does not destroy or cast aside His enemies, but by His Cross He draws all people to Himself. By His Cross — by His sacrifice of propitiation for your sins; and not only for your sins, but for the sins of the world — by His Cross, He has called you out of darkness into light, out of death into life, out of unbelief to faith, out of ignorance to the knowledge of the truth. It is by the Word of the Cross, therefore, that your brother is called from error to orthodoxy; not by violence or coercion, but by the powerful persuasion of compassionate forgiveness. Accompany your words with such compassion, and trust the Lord to vindicate you in the Resurrection of Christ from the dead.
Remember that the Lord has manifested His divine love for you, in that, while you were yet His enemy, Christ died for you. He has that very same love, also, for your brother: warts and all! Do you see your brother's sins and errors? Christ sees them, too, as well as He sees yours. And seeing them, He does not cast you away from His presence, but He moves to save you, both you and your brother. He does so by grace. That is the chief truth of the faith. Christ Jesus is the Savior of sinners. He has come not to call the righteous but sinners to Himself in repentance.
The Lord's desire for your brother is that he would receive and hold fast the forgiveness of his sins, which has already been obtained for him by the holy and precious blood of Christ, by His innocent suffering and death upon the Cross. That forgiveness of your brother's sins is one and the same forgiveness of Christ that you also depend upon for life and salvation. Therefore, irrespective of your brother's attitude toward you, whether or not he is willing to recognize his fault and receive your forgiveness, forgive your brother his trespasses against you.
Pray for your brother. Not in the way of the old Irish proverb, that God would either turn his heart or turn his ankle, but pray sincerely that your brother would be brought to repentant faith and sustained in the knowledge of the truth. It is almost impossible to retain any anger or bitterness toward someone, irrespective of the hurt that he or she may have caused, when you pray that Christ would deal with that person in accordance with His good and gracious will. You know that He desires all men to be saved, including your brother, so you can pray with absolute confidence for that. In addition, Christ has admonished you to pray for those who persecute you (and no less so for those who may not be persecuting you at all, but who are simply in error).
Pray for yourself, too, that the Lord would enlighten your mind with His Word and Holy Spirit, and that He would humble you unto repentance. Do not presume to contend for the faith by your own piety, holiness and willpower. Pride comes before a fall, but the Lord exalts those who humble themselves. Pray for that humility, therefore, and for the power of Christ that is made perfect in weakness. Pray that you may bear the Cross in such quiet and steadfast faith, that the world may see Christ Crucified in you and glorify the Father in Him.
Conduct yourself in fear and reverence, as all your thoughts, words and actions are carried out in the presence of God. Repent of your sins and return to the daily death and resurrection of your Holy Baptism. Speak only as the Lord your God has spoken to you. But do speak, always being ready to give a defense for the hope that is in you. Speak with charity, not only with your words but in your demeanor and by your actions, as one who is redeemed by the grace of God in Christ.
Forgiveness and charity do not require nor permit the tolerance of false doctrine. You rightly do contend for the faith in love for your brother, in love for the truth and purity of the Gospel, and in love for all your other neighbors in the world. But if your brother refuses to listen to you, be content with having spoken the Word of the Lord as clearly and faithfully as He has permitted. Rest in the knowledge that His Word, not your powers of persuasion, accomplish His intentions. And rejoice if you are counted worthy to suffer persecution for the sake of Christ and His Gospel. If you suffer on account of your own faults and failings, for those things repent; but for His Gospel, dare to risk all treasures, all comforts, pleasures and accolades. Contend only for the honor and glory of Christ Jesus, that His Name alone be great to the ends of the earth.
Not to us, O Lord, not unto us, but to Thee alone be all praise.