Here "this" refers to the question the Pharisees asked about Jesus eating with tax collectors and sinners.
# People who are strong in body do not need a physician, only those who are sick
Jesus answers with a proverb. He means that he eats with these kinds of people because he has come to help sinners. (See: [[rc://en/ta/man/translate/writing-proverbs]])
The phrase "need a physician" is understood. Alternate translation: "people who are sick need a physician" (See: [[rc://en/ta/man/translate/figs-ellipsis]])