The parable, which is the text of today, is exclusive to Matthew and contains the first of three parables. These parables are all addressed to the chief priests and elders of the people, as a continuation of Jesus’ response to their challenge of his authority. Since they remained silent to his earlier question about John the Baptist, the Matthean Jesus begins this parable by forcing them to answer. He does this through the question, “What do you think?” The older son is first asked to go and work in the vineyard. He initially refuses, but afterwards, relents and goes. Since the older son refused him at first, the father then goes to the younger son and asks that he go and work in the vineyard. This son replied that would certainly go, but did not do so. Without any doubt, the one who did the will of the Father was the older son who was asked first.
The Parable does not seem to be so much about Jew and gentile as it is about religious leader and public sinner. Thus, Jesus is saying that the scum of society, though it says no to God, repents, performs the Father's will, and enters the kingdom, whereas the religious authorities loudly say yes to God but never do what he says, and therefore they fail to enter.
Both religious leaders and public sinners had John as a pointer of the way to Jesus and the kingdom. Yet, of these, while the sinners repented and believed, the religious did not, even after seeing sinners repent.
Lip service is easy. It does not require any action on the part of the person who gives it. This kind of person merely says, but will not do. Committed service is more difficult, because this calls for action and putting oneself out for the sake of another. It is not those who say “Lord, Lord”, but those who DO what God wants, who will gain entry into the kingdom.