In Spite Of Their Claims To Be Otherwise They Should Recognise That They Were Simply As Bad As Their Fathers (23:29-33).
Along with their generation the Scribes and Pharisees made a great fuss about the godly of the past by erecting and decorating their tombs and monuments. It made them feel that they were not like their fathers who had disposed of the prophets and the godly. But at the same time they rejected John the Baptist and were intent on getting rid of Jesus. They did not realise that they were thereby guilty of rejecting Someone greater than the prophets, for they were not spiritually attuned. Thus Jesus points out that they were essentially just like their fathers.
Analysis
a “Woe to you, scribes and Pharisees, hypocrites! for you build the sepulchres of the prophets, and garnish the monuments of the righteous” (Matthew 23:29).
b “And say, ‘If we had been in the days of our fathers, we would not have been partakers with them in the blood of the prophets'.” (Matthew 23:30).
c “Thus you witness to yourselves, that you are sons of those who slew the prophets (Matthew 23:31).
b “Fill you up then the measure of your fathers” (Matthew 23:32).
a “You serpents, you offspring of vipers, how will you escape the judgment of Gehenna?” (Matthew 23:33).
Note that in ‘a' they try to make a great fuss of the righteous dead, and in the parallel they do so because they are like vipers trying to escape the judgment of Gehenna. In ‘b' they claim not to be like their fathers, and in the parallel Jesus tells them in fact that they really are, and sarcastically urges them to act accordingly (as they were in fact at this moment planning to do). Centrally in ‘c' is the fact that they are showing all the time that they are the sons of those who slew the prophets.