Those who were not highly regarded by most Jews are seen here coming near to Jesus "to hear Him." Their purpose is a noble one for they desire to be instructed by the Lord. The same cannot be said about the Pharisees and scribes who generally only listened to Jesus in vain hopes of finding something of which to accuse Him.
The religious leaders complained about Jesus' willingness to have fellowship with these sorts of individuals. They would never have any kind of social interaction with these people, primarily because they viewed them as unclean. They classified all as "sinners" who failed to observe the traditions of the elders, especially regarding purification. The tax collectors were also not regarded very highly because they were employed by the Roman government and thus viewed as traitors. Jesus not only received these people but also ate with them on a regular basis! The Pharisees and scribes do not believe such to be proper. Jesus speaks the following parables in answer to their objection:
"What man of you, having a hundred sheep, if he loses one of them, does not leave the ninety-nine in the wilderness, and go after the one which is lost until he finds it? And when he has found it, he lays it on his shoulders, rejoicing. And when he comes home, he calls together his friends and neighbors, saying to them, 'Rejoice with me, for I have found my sheep which was lost!' I say to you that likewise there will be more joy in heaven over one sinner who repents than over ninety-nine just persons who need no repentance" (Luke 15:4-7).
God has often expressed His love for mankind under the figure of a shepherd and sheep (e.g., John 10; Heb. 13:20; I Pet. 2:25). Men become lost by wandering away from the Creator and going into sin (cf. Isa. 59:1,2).
Jesus begins by asking them a personal question. He intends to refute their objection based upon what they specifically believe and practice. If any of these Pharisees or scribes were shepherds, they would leave the ninety-nine in their normal place of pasturage (i.e., "the wilderness" or a rural section of pasture land) and go searching for the lost sheep. Jesus is doing that very thing spiritually, yet they are murmuring against Him! They evidently understand the value of a lost sheep but not the value of a lost soul! They wouldn't want to lose even one physical sheep, and God doesn't want to lose any of His sheep either.
Once the lost sheep is found it will be brought back to the flock on the shoulders of the shepherd. The reason for this may have something to do with the weakness of the sheep and the affection of the shepherd, as well as the efficiency in returning to the flock in this manner.
The notifying of the shepherd's friends and neighbors of the restoration of the sheep to the flock indicates their knowledge of its loss. Had the Pharisees been "neighbors" to Jesus and shared in His desire to seek and save the lost (cf. Luke 19:10), they would have rejoiced with Him in His redemptive efforts.
"I say to you that likewise there will be more joy in heaven over one sinner who repents than over ninety-nine just persons who need no repentance" (Luke 15:7). The greater joy has nothing to do with a difference in value of a particular soul (cf. Acts 10:34,35) but with the emotion of the moment of restoration.
Jesus' point to the religious leaders is that a good shepherd will always search for a lost sheep and try to restore it, and that is exactly what Jesus is doing when he "receives sinners and eats with them"! The result of such would be "joy in heaven," but all these religious leaders could do was complain and find fault. This verse certainly does not imply that the Pharisees and scribes were among those who were not in need of repentance (cf. Luke 5:32). They may have fancied themselves to be in that position, but they weren't right before God (cf. Matt. 23).
Today, care should be given to each soul for every single one is important (cf. Matt. 16:26). To ignore the souls of those who may not be highly regarded by much of society is a sin of prejudice (cf. James 2:1ff).