A.T. Robertson Commentary Matthew 9:12

"But when he heard it, he said, They that are whole have no need of a physician, but they that are sick." — Matthew 9:12 (ASV)

But they that are sick (αλλα ο κακως εχοντες). Probably a current proverb about the physician. As a physician of body and soul Jesus was bound to come in close touch with the social outcasts.