Those whose lifestyle depicted that of open sinfulness were utterly rejected by the Jewish authorities. Neither would they allow for repentance on their parts, so they were astonished with Jesus’ willingness to mingle with them as though they were righteous. Therefore, Jesus responded to the Pharisees’ and rabbis’ attitude toward his policy of receiving publicans and sinners by speaking three parables, and, because Jesus directs his parables toward the scribes and Pharisees, they are depicted in them in a negative manner. Moreover, it is implied that the Jewish authorities would never have done what they see Jesus doing.
The first parable concerned sheep (Luke 15:3-7). Notice that before the one became lost, the whole herd of 100 sheep were together in the wilderness (Luke 15:4). The wilderness is a place where there was no specific path, and when he brought Israel out of the land of Egypt, they were guided by the Angel of the Lord. For 40 years he guided them there before he took them into the Promised Land. It was in this wilderness that Israel tempted God (Psalm 78:17-18, 40-41), and it was also in the wilderness that Jesus was tempted (Luke 4:1). Nevertheless, although he was tempted there for 40 days, he was tempted pretty much throughout his public ministry. Neither was he tempted in a literal wilderness. Instead, Jesus preached the word of God in the wilderness of people (Ezekiel 20:35), a people who didn’t know God and didn’t know how to relate to him.
Once Moses thought he needed a relative (i.e. through his wife) to guide him in the wilderness (Numbers 10:29-32), but, even while that discussion was going on, the Lord caused the priests to rise up and carry the ark before Israel for three days (Numbers 10:33). In so doing, Moses came to realize all he needed to do was trust the Lord to lead Israel through the wilderness. With this in mind, the shepherd was the guide for his sheep in the wilderness (Luke 15:4), but, as sheep are wont to do, one wondered away, and the shepherd left the herd to find the one sheep who wondered away.
This is what Jesus had done. He had left the ninety nine righteous, viz. the Jewish authorities and those who listened to them, and sought after the one who wandered away (Luke 15:4), viz. the publicans and sinners who desired to listen to him (Luke 15:1). Jesus left the righteous in order to find the lost in order to save them from further harm. Jesus is the Way through the wilderness, and only those who trust in him are able to find the Way into the Kingdom of God (the Promised Land).
Moses claimed that a Prophet would arise out of the people of Israel one day, and this Prophet would be like Moses (Deuteronomy 18:15-19), in that he would have the word of the Lord and be able to lead the people. It was not only expected but also commanded that Israel would listen and obey this man. If they refused, their decision would be upon their own heads. The fact that the scribes and Pharisees refused to consider Jesus’ words, shows they put their own ideas before the word of God (Luke 5:39). In rejecting Jesus, they had rejected the Straight Gate into the Promised Land or the Kingdom of God. It was as though they refused their Guide / Shepherd, who led them in the wilderness.
In Matthew Jesus claimed that the Jewish authorities had laid many burdens upon the shoulders of men (Matthew 23:2-4), and this they supposed served God, whom they understood to be a cruel taskmaster. On the other hand, Jesus, claiming to bring good news from God, said he, the Shepherd of the flock, bore those burdens out of compassion for his disciples, and this served God’s purpose.
It seems to me that in using the term righteous or just persons (G1342) in Luke 15:7, Jesus is using the term ironically rather than as a sincere estimation. After all, in receiving the publicans and sinners, he was of necessity leaving the scribes and Pharisees behind, not his choice but theirs. They simply would not follow. The great value that Jesus placed upon the single sheep over the ninety-nine (Luke 15:4) is that it represented the one who desired to listen to Jesus, while the ninety nine represented the scribes and Pharisees who had rejected him as their Messiah. They refused to admit that they were also sinners and needed a Savior.