Now his elder son was in the field: and as he came and drew nigh to the house, he heard musick and dancing.
Note 6 at Lu 15:25: This parable of the prodigal son is a great example of God's willingness to forgive and restore the sinner. However, that was not the main point that Jesus was making through this parable. This parable, as well as the parables of the lost sheep (Lu 15:3-7) and the lost coin (Lu 15:8-10), was in response to the Pharisees murmuring about Jesus receiving sinners and eating with them (Lu 15:2). Jesus was using this parable to rebuke the Pharisees for their harsh, self-righteous, and unforgiving attitude toward sinners.
The older brother in this parable was symbolic of the Pharisees. Like this brother, the Pharisees had not lived outward lives of rebellion, and they thought that others who didn't measure up to their standard were surely hated by God. But "God so loved the world" (Joh 3:16), and "Christ Jesus came into the world to save sinners" (1Ti 1:15). Just as this older brother was self-centered and jealous, the Pharisees were not operating in the love of God toward sinners, because they were so in love with themselves. They resented Jesus giving the sinners what the Pharisees thought they themselves deserved.
The older brother had not wasted his father's money on harlots, but he had not been serving his father from his heart either. As can be seen in Lu 15:29-30, this brother had remained at home and served his father because of the recognition he received. The younger brother who had sinned greatly was coming to his father in humility with a pure heart of repentance, and that was more acceptable to the father than the older brother's "lip service."
The older brother cited his own goodness just like the Pharisees trusted in their own righteousness (Lu 18:9, Ro 10:3, and Php 3:9). This self-seeking, self-righteous attitude is the greatest sin of all and what Jesus was rebuking (see note 8 at Lu 15:29).