Matthew Henry on Matthew 21:28-32

Parables which give reproof, speak plainly to the offenders, and judge them out of their own mouths. The parable of the two sons sent to work in the vineyard, is to show that those who knew not John's baptism to be of God, were shamed by those who knew it, and owned it. The whole human race are like children whom the Lord has brought up, but they have rebelled against him, only some are more plausible in their disobedience than others. And it often happens, that the daring rebel is brought to repentance and becomes the Lord's servant, while the formalist grows hardened in pride and enmity.