How did the Pharisees react to believers embracing Christ as Messiah?
The Pharisees became angry when they saw believers embracing Christ as Messiah. Their self-righteous mentality, typified by the older brother, led them to oppose and persecute these believers, seeking to stamp them out, even putting them to death and in prison, as illustrated by Saul of Tarsus.
Les explains that the older brother in the parable is typical of the Pharisees in Israel. Although they had been under the covenant promises like the other brother, they were so self-righteous and filled with their own importance, pomp, and circumstance that they saw no need of anything. When they saw the little element of believers embracing Christ as the Messiah, it made them angry. Like Saul of Tarsus, who is typical of this mentality, they thought they could stamp them out by putting them to death and in prison. Les connects this to Jesus' statement that the well person doesn't need a physician, but the sick person does. Paul makes it plain that you cannot be saved if you think you're going to make it on your own; you must come as a sinner, which is mandatory.