"I saw them eating and I knew who they were." That saying, or some version of it, is well-known now. And it certainly describes the Pharisees whom we encounter in Luke 15:1-2. Jesus was welcoming the very folks whom the religious establishment had written off. Worse, he was at table with them, which was an intimate act of fellowship that implied a kind of personal bond and connection. So we're told the Pharisees muttered into their beards about this. Jesus overheard their comments and knew their hearts and so told them three stories that reveal the heart of God.
And that's really what is going on in Luke 15: we're not here first of all being given stories of the "go and do likewise" variety. The parable in verses 11-32 is not in Scripture first of all to encourage fathers to be forgiving of their naughty kids any more than the first two stories were an instruction to shepherds or a cautionary tale to take better care of your fiscal assets. No, all three reveal the heart of God — a heart that is broken clean in two by lostness but a heart that sings with a joy as wide as the cosmos when even the silliest sheep or the meanest of sons comes back and/or is found again.