The theme is the natural tension between grace and works that we find throughout the faith. Paul seems to be the champion of grace. Peter and others appear to speak strongly of the need for works. Of course, I am not sure the actual division at that time was quite that clear cut. Paul certainly gave us several lists of things (works and lifestyles) which he said plainly were not acceptable to God. While Peter, for example, accepted plenty of things by grace through faith that denied the whole notion of works – such as gentiles being saved.
Here again, Jesus shows the way.
The chief priests and elders came to question his authority, but he deftly walks around the question and poses one in turn. Which of the two sons did what the father asked? Clearly the first. The second said the right words, may have believed them strongly, but in the end he did not do the work. Jesus here is saying to his children, you must do.
One thing often missed. Both children in the story are sons of the father. That is not the issue. What Jesus was pointing out was the prostitutes and tax collectors eventually did the father’s will. The chief priests and elders did not, and still did not.
I think here is where we might tweak that famous passage in James where he says faith without works is dead. Let us say instead that it is their lifestyle, their works that show the faith people really have. What a person does will always be true to what is actually in the heart.
Let me add my voice to the prophets and apostles. A person may have all the right and holy words, they may speak fluent Christianese, and they may have actually convinced themselves that they are good Christians, true believers, children of God. But I would suggest looking at their life. Just because a person goes to church on Sunday, it does not alow them the grace to treat people like dirt Monday through Friday.
Do not be fooled by the sincerity of the words. If the faith is true, it will show itself in works, even if at first they say, “No, I’m not going…” There is always hope for sinners, and room to repent and go do what the father asks. But make no mistake. The point is to do what God commands. Nothing less.