This is an important question, not simply for understanding the background of this particular text. Christians often shrug off questions of public ethics because we say, "Why should we expect lost people to act like Christians?" I once heard a prominent preacher say that it didn't matter to him if his neighbors went to hell as prostitutes or as policemen; it only mattered that they were going to hell.
In one sense, this is a good impulse. After all, Jesus never acted shocked or appalled by the behavior of the lost people. Jesus spoke with gentleness to the lost sinners around him, but with severity at religious leaders, hiding their sin behind religiosity and using their positions to serve selfish interests.
And the apostle Paul wrote that he didn't judge "outsiders" but instead that it is those "inside the church whom you are to judge" (1 Cor. 5:12). The gospel didn't come to achieve a society of morally straight people unreconciled to Christ.
But, if all that's true, why does John persist in calling out this obviously unregenerate political leader for his sexual behavior? John isn't incidental to the biblical story. Jesus calls him the greatest of the prophets.
Obligation of a King
This wasn't really a question of merely personal behavior by an outsider. Herod was clearly a pagan internally, but he held an office instituted by God, an office with obligations for obedience to God. The rulership over Israel, after all, wasn't the equivalent of the queen of England or the president of the United States. Israel was a covenant nation of priests. The king was to be of the house of David, and he was to model the line of Christ.
In the same chapter of Deuteronomy that the apostle Paul quotes to speak of internal church discipline, the law lays out the qualifications for king. He shouldn't use the office to serve his appetites for things or for sexual gratification (Deut. 17:17), but ought to meditate on the Word of God and act according to it "that his heart may not be lifted up above his brothers, and that he may not turn aside from the commandment, either to the right hand or to the left" (Deut. 17:20).
Not Merely Private Morality
This was a question of public justice, not merely of private morality. Herod's sin was multifaceted. Yes, it was a private act of sexual immorality, taking as his own a woman he shouldn't have. But Herod was acting not just as a man but as a ruler.
Herod, of course, was a puppet king, acting as a client of the Roman Empire. He couldn't have provided what he offered in his sexually ignited boast of giving Herodias's daughter "up to half my kingdom" (Mk. 6:23). Herod didn't have the same power as David, but it was the same principle at work. David's taking of Bathsheba was more than just an immoral use of his private parts, but an immoral use of his public office.
We can all see what this means, even apart from divine revelation. One of the good things the feminist movement has brought to us is the way we deal publicly now with sexual harassment. An employer who pressures an employee for sexual favors isn't just an immoral person; he is misusing power. When the CEO sleeps with an intern, his offense isn't just against God and his wife, but is also an unjust abuse of power.
In line with all the prophets before him, John spoke out against the powerful misusing their privilege to exploit the vulnerable. Think of Daniel telling Belshazzar that the "writing is on the wall" for his prideful kingdom's fall or Isaiah speaking truth to power to those who "rob the poor" and "make the fatherless their prey" (Isa. 10:2). Think of, after John, Jesus' brother James denouncing the landowners who exploit workers with unjust wages (Jas. 5:4-6).
John risked his neck to speak on this question not just to Herod as king but also to Herod as a man. Paul doesn't "judge" the pagan outsiders, that's true. He means that there is no means of holding those outside the church to the accountability of church discipline. But the church can still discern between good and evil. Even as Paul calls out the sin of the church member in Corinth, he compares it to the moral climate of the "pagans" on the outside (1 Cor. 5:1).
Jesus deals gently with tax collectors and sinners. He doesn't, as he does with the religious leaders, call them whitewashed tombs or turn over their market tables. But he doesn't refuse to speak to their sin. When he meets the woman at the well, he isn't shocked by her serial monogamy, but he doesn't leave it unquestioned either. He asks her, "Where is your husband?"
Those outside the church aren't our battlefield but our mission-field, that's true. We shouldn't rail against them as though they are somehow different than we are, apart from God's mercy in Christ. But the gospel is to be pressed on all creatures, on every human conscience. And the gospel is a call not only to faith but also to repentance. God now "commands all people everywhere to repent, because he has fixed a day on which he will judge the world in righteousness by a man whom he has appointed," (Acts 17:31), Paul preached at Mars Hill.
We then speak to lost people not only of the historical truth of Jesus' life, death, and resurrection, and not only of his grace and mercy in receiving sinners. We also call them to turn from sin, and to agree with God that such sin is worthy of condemnation. Without this, there is no salvation. We speak then, as the apostle did to a pagan ruler, about "righteousness and self-control and the coming judgment" (Acts 24:25).
Our lost neighbors might be "pagan" in the sense that they are not part of the community of God, but they are still accountable before God. Their consciences are embedded with a law. John wasn't the first to say to Herod that he couldn't have his brother's wife; this was hardly new information. Herod's conscience already told him that much, and pointed him to his accountability on the day of judgment. John's rebuke was an essential part of gospel preaching.
Christians often ping back and forth between extremes. The church of the last generation was often more concerned with a moral majority than with a gospel priority. In our attempt not to fall into that error, we could fall into an opposite, and just as dangerous, ditch. We could assume that all moral norms speak merely internally to the church, and we could fail to speak to unbelievers about such things. Such would be a refusal to love our neighbors, to warn them of what we will face at the judgment seat. But it would also be a refusal to preach the gospel. Without defining sin and justice, we cannot offer mercy.
Guilty consciences don't initially like that word. None of us did, at first. But that's the mission we've been given. Some of us may wind up with our heads on silver platters. Jesus knows how to put heads back on.