The message of Jesus in this parable is as clear to us as it would have been to those original hearers. God desires us to act on the faith we profess. Additionally, vain lip service is insufficient to please God. If I tell God I will do something but don’t follow through, I have disobeyed. This was precisely the sin of the Pharisees. They loved to claim to obey God, but they rejected Jesus. At the same time, those who were the rebels of society and had mocked God in their living repented and obeyed.
There is one more thing about this simple parable that we should remember. The response of the first son is shocking! We might miss it if we are not careful, but this son literally tells his father NO. Now, we live in a culture where that is far too commonplace, but Jesus was speaking to a culture that would have been shocked. Deuteronomy 21: 18-21 says, "If any man has a stubborn and rebellious son who will not obey his father or his mother, and when they chastise him, he will not even listen to them, then his father and mother shall seize him, and bring him out to the elders of his city at the gateway of his hometown. They shall say to the elders of his city, 'This son of ours is stubborn and rebellious, he will not obey us, he is a glutton and a drunkard.' Then all the men of his city shall stone him to death; so you shall remove the evil from your midst, and all Israel will hear of it and fear.” You and I deserve death, yet we have been given unimaginable grace.