This was the Feast Day of St. Matthew, and the reading was Matthew 9:9-13. Not too long before this, I'd read the parallel account in Mark 2:13-17. I felt that something was off about the structure of "'Those who are well have no need of a physician, but those who are sick'" (in verse 17), but it wasn't until hearing the same construction in Matthew (in verse 12) that I had some insight into it.
What had puzzled me is that there are some implied words in the second clause: "Those who are sick [have need of a physician]." I'd understood the meaning, of course; I simply hadn't understood what was going on in the grammar.
Consequently, I realized that such an ellipsis is significant. In the same way that the phrase "those who are sick" requires the implied words in order to form a complete clause, the sick people need the treatment of a doctor in order to become healthy.
