Luke 15:8
4 “Which one of you, if he has a hundred sheep and loses one of them, would not leave the ninety-nine in the open pasture and go look for the one that is lost until he finds it? 5 Then when he has found it, he places it on his shoulders, rejoicing. 6 Returning home, he calls together his friends and neighbors, telling them, ‘Rejoice with me because I have found my sheep that was lost.’ 7 I tell you, in the same way there will be more joy in heaven over one sinner who repents than over ninety-nine righteous people who have no need to repent. 8 “Or what woman, if she has ten silver coins and loses one of them, does not light a lamp, sweep the house, and search thoroughly until she finds it? 9 Then when she has found it, she calls together her friends and neighbors, saying, ‘Rejoice with me, for I have found the coin that I had lost.’ 10 In the same way, I tell you, there is joy in the presence of God’s angels over one sinner who repents.”
Song of Songs Rabbah 1:9
AggadahR. Phinehas b. Jair opened his exposition with the text, If you seek her as silver, etc. (Prov. 11:4). If you seek after words of Torah as after hidden treasures, the Holy One, blessed be He, will not withhold your reward. If a man loses a small coin in his house, he lights lamp after lamp, wick after wick, until he finds it. Now does it not stand to reason: if for these things which are only ephemeral and of this world a man will light so many lamps and lights till he finds where they are hidden, for the words of the Torah which are the life both of this world and the next world, ought you not search as for hidden treasures? Hence ‘if you seek her as silver, etc.’ R. Eleazer said: Never in my life has anyone been before me at the Beth Hamidrash, nor have I gone out leaving anyone there.
Notes and References
"... This triadic interpretation is more concisely summed up by the concluding refrains of Luke 15:7 and 10, which contrast (a) the joy in heaven over (b) one sinner who repents with that for (c) those who need no repentance. Since these refrains clearly establish the allegorical referents of the three main characters, they are widely assumed to be secondary additions to the parables.[61] But Bailey has shown the integral part the conclusions have in the structures of the overall passages. As noted above (5.2.3), the lost sheep is a brief three-stanza poem in which Luke 15:7 (stanza 3) balances the first part of Luke 15:4 (stanza 1). Some find unbearable tension between the shepherd (or woman) searching and finding the entirely passive sheep (or coin) in Luke 15:4-6 (and 8-9) and a sinner’s more active repentance (Luke 15:7, 10), yet this is precisely the kind of tension between divine sovereignty and human response which characterizes much of Scripture.[63] Luke 15 as a whole reproduces the tension here, with the lost sheep and coin stressing God’s saving initiative and the prodigal son highlighting the need for repentance as well. “Parallels” to these two parables in the ancient Mediterranean world consistently alleviate this tension by making the lost sheep or coin worthy of special attention. We have already noted above (2.2.2.1.2) the rabbinic parable in which a lost coin stands for the priceless Torah ..."
Blomberg, Craig L. Interpreting the Parables (pp. 60-61) InterVarsity Press, 1990