Klyne Snodgrass, in Stories with Intent, turns to a chp on “parables of lostness” and it begins with the parable of the lost sheep.

3 Then Jesus told them this parable: 4 ?Suppose one of you has a hundred sheep and loses one of them. Does he not leave the ninety-nine in the open country and go after the lost sheep until he finds it? 5 And when he finds it, he joyfully puts it on his shoulders 6 and goes home. Then he calls his friends and neighbors together and says, ?Rejoice with me; I have found my lost sheep.? 7 I tell you that in the same way there will be more rejoicing in heaven over one sinner who repents than over ninety-nine righteous persons who do not need to repent.

Here’s my own question: Why do you think, when the meaning of a parable is relatively clear and easy to interpret, we have such a difficult time living it out? (As is the case with this parable; easy to see, hard to do.)
This parable, with its twin lost coin, is a prelude to the parable of lost son. The parable is an interrogative parable.
On “background” — some good stuff from the OT and NT; nice collection of stuff form Qumran and early Christian writings and later Jewish writings. (I can’t cite this stuff; this section alone will save preachers and students oodles of leg work.)
He then compares Matthew 18’s account with Luke 15; “relatively little in common.” Two independent accounts of the same parable. He’s got good common sense about whether or not the parable is a chiasm — repetition in inverse order — and he thinks one needs to stretch the evidence to find it; and today many are prone to find chiasms everywhere, and more often than not the interpreter has to use his or her own words to make it work.
The code of not associating with sinners is written into the fabric of the parable; shepherding was a despised trade; good size flock for the shepherd; lost sheep give up and don’t try to find their way back, perhaps explaining why the shepherd has to carry the sheep.
Meaning: the act of the shepherd, though odd, is not absurd; this is not the point of the parable. I like this: “This parable does not care about any of these questions.” There is some allusion to Ezek 34 and only maybe Ps 23. Bailey overdoes it.
The point is the deliberate association of Jesus with sinners. God is at work through Jesus to forgive and restore his people. God is a forgiving, gracious God. Repentance is the act of humans in response to God’s grace. The parable also has joy as a theme.
“God is not passive, waiting for people to approach him after they get their lives in order. He is the seeking God who takes the initiative to bring people back, regardless of how ‘lost’ they are.”
Jesus’ behavior, grounded in God’s, is at variance with the religious experts. Potent deconstruction of religion that does not work out the very character of God in relationship to those who are sinners.
How can we let our behavior be more shaped by God’s?