Luke just recorded that Jesus called a would-be disciple to pay attention to what He said ( Luke 14:35). Now he noted that many tax collectors and "sinners" were doing precisely that. Thus he presented that group of needy spiritual outcasts as responding to Jesus" ministry. However, he also noted, in contrast, that the Pharisees and scribes were critical of Jesus (cf. Luke 5:29-30). They were not really listening to Him. Probably he balanced two positive groups (tax gatherers and sinners) with two negative groups (Pharisees and lawyers) to heighten the contrast further. Receiving and eating with sinners demonstrated openness to them and fellowship with them. [source][source][source]
"The sinners were the immoral or those who followed occupations that the religious regarded as incompatible with the Law." [1][source]
The following parables taught the religious leaders that sinners" return to God should be a cause for rejoicing rather than grumbling (cf. Luke 19:7). One writer titled these parables "The Searching Shepherd," "The Searching Woman," and "The Seeking Father." [2] Shepherds, unmarried maidens, and rebellious sons were all examples of disenfranchised people who were usually excluded by the religious establishment of Jesus" day. [3] The first parable emphasized the lost condition, the second the search, and the third the restoration. [2]2 [source]