This was Christ’s response to those who questioned why he associated with sinners, even eating and drinking with them. He had come to call sinners to repentance. Those who thought themselves righteous, as the Pharisees did, would not answer the call. Only those who admitted their sin would hear and obey his call.
This is still Christ’s ministry. As the Father sent him, he sends us (John 20:21). Having repented of our sins and believed in Jesus, we are sent to call sinners to repentance too.