Does true evangelism mean that Christians may proclaim the Gospel indiscriminately? Here are some thoughts on the matter from Luther, Chemnitz and Walther.
LUTHER [AE 45:71]
In the second place, if you want to handle the Gospel in a Christian way, you must take into account the people to whom you are speaking. These are of two kinds. On the one hand, there are those who are hardened and will not listen, and who, in addition, deceive and poison others with their lying mouths. Such are the pope, Eck, Emser, and some of our bishops, priests, and monks.
You should not deal with them at all, but hold to the injunction of Christ in Matthew 7[:6], “Do not give dogs what is holy, and do not throw pearls before swine, lest they trample them underfoot, and the dogs turn to attack you.” Let them remain dogs and swine; they are a lost cause anyway. And Solomon says, “Where there is no hearing, pour not out words.39 But when you see that these same liars pour their lies and poison into other people, then you should boldly take the offensive and fight against them, just as Paul in Acts 13[:10–11] attacked Elymas with hard and sharp words, and as Christ called the Pharisees a “brood of vipers” [Matt. 23:33].
You should do this, not for their sake, for they will not listen, but for the sake of those whom they are poisoning. Just so does St. Paul command Titus to rebuke sharply such empty talkers and deceivers of souls [Titus 1:10–13]
CHEMNITZ [Loci Theologici, CPH/J.A.O. Preus translation, p. 546]
The hearts of men by nature are either pharisaic or Epicurean. For the Pharisees the doctrine of the Gospel is something unpleasant, because they believe that by their own purity they are righteous before God and therefore there is no need for that righteousness of which the Gospel speaks. From such people we must on the basis of Scripture take away all trust in their own righteousness before God, and they must be confined by the Law under sin [Gal. 3:22]. But the Epicureans, when they hear about the righteousness of the Gospel, are not seriously concerned, and do not seek or embrace or cling to it, because they are convinced of the idea that what we are like and how we live are of no importance before God, whether we are reconciled with God or not. If we immediately set before them the promise of the Gospel, it accomplishes no more than casting pearls before swine. Therefore we must denounce such people as sinners on the basis of the Word of God, for he who has not been reconciled with God through Christ is under the frightful wrath and curse of God, he is in the kingdom of Satan and in the power of darkness, and nothing is more certainly expected for him than the judgment of eternal damnation.
This is the preparation for grace, as Luther says in discussing Galatians 3, for which the Gospel uses the ministry of the Law, so that both repentance and remission of sins will be preached in the name of Christ. We must preserve this order in teaching the doctrine of justification, so that all, whether Pharisees or Epicureans, might be moved by the Holy Spirit not to despise, neglect, hate, or attack the righteousness of the Gospel, but might hunger and thirst for righteousness, that is, that they might love, seek, embrace, and hold fast the grace and mercy of God which the Gospel offers and shows to us in Christ. The Son of God Himself used this method both in His formal teaching (as in Mark 1:15, “Repent and believe the Gospel”; cf. Matt. 4:17) as well as in His pastoral practice, so to speak, as when He treats Mary Magdalene one way and the Pharisee another [Luke 7:36 ff.]. It is worthy of note that the same question is asked in Matt. 19:16; Luke 10:25; Acts 2:37; and 16:30: “What must I do to be saved?” But because in Acts the question is asked by those who are contrite, while in the gospels by Pharisees, therefore the answer is not the same, and yet the purpose is the same in both cases.
WALTHER [Law and Gospel, Dau translation, p. 113]
Matt. 7:6 our Lord says to His disciples: Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet and turn again and rend you. A remarkable utterance! What is meant by “that which is holy”? Nothing else than the Word of Christ.
What is meant by “pearls”? The consolation of the Gospel, with the grace, righteousness, and salvation which it proclaims. Of these things we are not to speak to dogs, that is, to enemies of the Gospel; nor to swine, that is, to such as want to remain in their sins and are seeking their heaven and their bliss in the filth of their sins.
Isaiah says, chap. 26:10: Let favor be showed to the wicked, yet will he not learn righteousness. In the land of uprightness will he deal unjustly and will not behold the majesty of the Lord. It is quite useless to offer mercy to the godless. They imagine either that they do not need it or that they already have all of it. The trifling sins, they say, of which they are guilty have long been forgiven, and grass has grown over them. To a person of this stripe I am not to preach the Gospel; in other words, I am not to offer him mercy -- for that is what preaching the Gospel means -- because he will not be benefited by it.
A wicked person, who wants to remain in his sins, whether they be gross or refined sins -- for the devil can bind men not only with the ropes of filthy, gross sins, but also with such delicate threads as pride, envy, lovelessness -- such a wicked person, Isaiah says, does “not behold the majesty of the Lord.” He does not see what a great treasure is offered him. He does not understand the doctrine of salvation by grace; either he spurns it, or he shamefully misapplies it. He thinks: “If mere faith is all that is necessary for my salvation, my sins, too, are forgiven. I can remain such as I am, and I shall still go to heaven. I, too, believe in my Lord Jesus Christ.” The preacher who is to blame when secure sinners misapply the Gospel loads himself with a great guilt and responsibility before God.