It should not seem odd that we ask sinners to repent. Jesus did. And if they did not repent, he predicted they would perish (Luke 13:3,5). Repentance is a change of heart that leads to a change of behavior.
Were we to preach righteousness to a drunkard, we would expect him to repent. In his repentance, he would truly sorrow for his sin, long for righteousness and to please God, and give up his bottle.
Should that drunkard say to us, "I not at all sure that the bottle is sinful. I'm not sure I need to give it up. You are merely pressing your tea-total tradition on me. I am a saved person depending on the grace of God just like you. How dare you judge me for drinking; you are the one who ought to give up your judgmental ways!" The guilty always turn it upon the innocent.
My friend, how seriously would we take that drunkard? Would we not quote to him what the Lord said about the matter (1 Cor. 6:9-1o; Gal. 5:19-21). It is obvious that here is a person who has deceived himself into thinking that he can continue as a drunkard and still have the approval of God. Paul's admonition "be not deceived" is given because people do indeed deceive themselves.
To give approval and fellowship without repentance is to deceive ourselves and to cheat God. We must not deceive ourselves. God won't excuse us and look the other way, while we excuse others.
Those who use instruments in Christian worship have no desire to give it up. Neither did Ahaz. Just because they don't think it is wrong doesn't change things. Error is still error, even if we deny or ignore it.
I am more troubled by the Urijahs (2 Kings 16:10-16) among us, who go along silently and will not speak against the humanly devised altar of our time. By their unwillingness to offend men, they move over the altar of God for the Damascus reproduction. They are more than willing to "get along" and apologize for others' bad attitudes than they are to speak out against the sin.
The instrumentalist says, "I am not at all sure the instrument is sinful. I am not sure I need to give it up. You are merely pressing your a cappella tradition on me. I am a saved person depending upon the grace of God just like you! How dare you judge me for using an instrument; you are the one who ought to give up your judgmental ways."
It is one thing to depend upon the grace of God in repentance, however, and another to presume upon the grace of God with an attitude of self-deception about what is and is not sin. All my wishing doesn't change God's will. All my blaming doesn't remove my responsibility.
Appealing to God's grace does not substitute for repentance--not for the drunkard, not for the instrumentalist, and not for the compromiser who approves error. Jesus meant what he said in Luke 13:3.
loving enough to tell the truth.