Jamieson, Fausset and Brown on Matthew 21:30

30. And he came to the second, and said likewise. And he answered and said, I go, sir--"I, sir." The emphatic "I," here, denotes the self-righteous complacency which says, "God, I thank thee that I am not as other men" (Lu 18:11).

and went not--He did not "afterward repent" and refuse to go; for there was here no intention to go. It is the class that "say and do not" (Mt 23:3)--a falseness more abominable to God, says Stier, than any "I will not."