When faced with irrefutable proof that a professing Christian is in open sin, why do they not see this and refuse to repent?
Luke answers the question for us. Well, at least it’s part of the answer.
When they heard these things they fell silent. And they glorified God, saying, “Then to the Gentiles also God has granted repentance that leads to life.”
As is clearly indicated, repentance is a gift from God. God grants, or gives, this gift of repentance that leads to life. If God doesn’t give it than we can’t expect anything less than an unrepentant individual (sinner).
Christianity has a great plan for dealing with folks who profess Christ yet refuse to repent when confronted with their sin. Basically we are to shun these unrepentant sinners in order to shame them in order to hopefully bring about their repentance.
1 Corinthians 5: 11 states the following command;
But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler–not even to eat with such a one.
The Greeks have a saying that goes like this : “a man who eats alone has no friends” so when a Greek sees someone dining alone, usually that person will be invited to dine with them. This was especially true in Paul’s day (that’s where the saying came from or so I’ve been told) so for Paul to command that they not even eat with the man meant something. The unrepentant person claiming to be a brother was to be shunned which would hopefully bring about shame which might bring them to repentance.
John Calvin has a similar opinion;
A third end of discipline is, that the sinner may be ashamed, and begin to repent of his turpitude. Hence it is for their interest also that their iniquity should be chastised, that whereas they would have become more obstinate by indulgence, they may be aroused by the rod. This the apostle intimates when he thus writes —“If any man obey not our word by this epistle, note that man, and have no company with him, that he may be ashamed” (2 Thess. 3:14). Again, when he says that he had delivered the Corinthian to Satan, “that the spirit may be saved in the day of the Lord Jesus” (1 Cor. 5:5); that is, as I interpret it, he gave him over to temporal condemnation, that he might be made safe for eternity. And he says that he gave him over to Satan because the devil is without the Church, as Christ is in the Church. Some interpret this of a certain infliction on the flesh, but this interpretation seems to me most improbable. (August. de Verb. Apostol. Serm. 68)
Calvin, J., & Beveridge, H. (1997). Institutes of the Christian religion. Translation of: Institutio Christianae religionis.; Reprint, with new introd. Originally published: Edinburgh : Calvin Translation Society, 1845-1846. (IV, xii, 5). Oak Harbor, WA: Logos Research Systems, Inc.
The only way any of this could possibly work is it must be done in community. Those communities were supposed to be their local assemblies. If a man wasn’t part of the local assembly than there was probably little chance this method would work. Then again if someone claimed to be a brother in Christ and refused to fellowship with other believers then they’d be looked on with suspicion. Like I said before these folks did things together.
Matthew tells us there is another possibility as to why folks refuse to repent:
“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’
I doubt this will come as a surprise to anyone reading this but not everyone claiming Christianity actually is. They may think they are, and even do great things in Christ’s name, but they weren’t granted the gift of repentance. Jesus tells us we will know them by their fruits (Matthew 7:20) one of those being fruits of repentance (Luke 3:8).
That’s what I see the bible teaching on this matter. Hopefully others will weigh in so you can get a fuller answer to your question!