Luke 15:32

It was meet that we should make merry and be glad. For the most convincing of reasons, because this my son, thy brother, who was dead in trespasses and sins, is now restored to grace and favour, wherefore it behovest thee to take part in our rejoicing, and not to be envious and to murmur against him.

Christ now leaves the Pharisees to apply the parable to themselves. For, says Theophylact, "It is intended to teach that although we may be just, we must not cast off sinners nor murmur because God receives them;" and again, "The Lord speaks as it were after this manner; I beseech you who are righteous and free from reproach, that ye murmur not at the salvation of sons, for this prodigal is still a son."