In his response Jesus uses the image of a doctor (physician). A doctor is not called to healthy people, but to sick people. This is exactly how Jesus came for sinful people. But then you must be willing to admit that you are a sinner, just like a sick person must admit that he is sick! The leaders of the people lacked this. They considered themselves healthy, that is, righteous before God.
17 Jésus ayant entendu cela, leur dit: Ce ne sont pas ceux qui se portent bien qui ont besoin de médecin, mais les malades. Je ne suis pas venu appeler des justes, mais des pécheurs.