The mention of the son's longing to eat with the swine in Luke 15:16 could refer to how the Pharisees viewed the sinners (and Christ, for eating with them) in Luke 15:2.
The father, who represents our Heavenly Father, implies to the older son that his love for both sons is not dependent upon their perfection, but their willingness to return to Him with a broken heart and a contrite spirit.