Luke indicated that Jesus answered them (καὶ ἀποκριθεὶς ὁ Ἰησοῦς). He said to them (εἶπεν πρὸς αὐτούς) that those who are well (οἱ ὑγιαίνοντες) do not need a physician (Οὐ χρείαν ἔχουσιν…ἰατροῦ). However, those who are sick do need one (ἀλλὰ οἱ κακῶς ἔχοντες). Mark, chapter 2:17, and Matthew, chapter 9:12, are almost word for word to Luke, so that Mark might be the source of this saying. Mark and Matthew said that Jesus heard what the Pharisees were saying to his disciples. Jesus responded to them that the well people or strong ones did not need a physician or medical doctor, but the sick did. As Pope Francis likes to say, the Church is a mobile ambulance, not a hospital waiting for people to come in. Jesus saw his mission as reaching out, rather than expecting people to come to him.
This response of Jesus is almost the same as in Mark, chapter 2:17, and Luke, chapter 5:31-32. Jesus heard (ὁ δὲ ἀκούσας) what the Pharisees were saying to his disciples. He responded that the well people or strong ones do not need (εἶπεν Οὐ χρείαν ἔχουσιν οἱ ἰσχύοντες) a physician or medical doctor (ἰατροῦ), but the sick do (ἀλλ’ οἱ κακῶς ἔχοντες). As Pope Francis likes to say, the Church is a mobile ambulance, not a hospital waiting for people to come in.