What is the parable of the two sons?
The parable of the two sons was spoken by Jesus Christ and is recorded in Matthew 21:28-32. The two sons begins in Matthew a series of denunciations addressed to the Pharisees. Its drift is plain.
These "hypocrites" profess to keep God's law and break it; hence their scorn of the of the preaching of John the Baptist; whereas "publicans and harlots" were converted; therefore they shall go into the Kingdom before the others.
But if it be accommodated to Jews and Gentiles, who is the elder son who the younger? From the text no reply can be drawn and commentators are not agreed. In some manuscripts the order is reversed, but without foundation. (See Luke 7:29-30, 37-50)
28 But what think ye? A certain man had two sons; and he came to the first, and said, Son, go work to day in my vineyard.
29 He answered and said, I will not: but afterward he repented, and went.
30 And he came to the second, and said likewise. And he answered and said, I go, sir: and went not.
31 Whether of them twain did the will of his father? They say unto him, The first. Jesus saith unto them, Verily I say unto you, That the publicans and the harlots go into the kingdom of God before you.
32 For John came unto you in the way of righteousness, and ye believed him not: but the publicans and the harlots believed him: and ye, when ye had seen it, repented not afterward, that ye might believe him.
International Standard Bible Encyclopedia, which is in the public domain (with minor edits).