Albert Barnes on Luke 14:3

Jesus, answering. To answer, in the Scriptures, does not always imply, as among us, that anything had been said before. It means often merely to begin or to take up a subject, or, as here, to remark on the case that was present.

Is it lawful, &c. He knew that they were watching him. If he healed the man at once, they would accuse him. He therefore proposed the question to them, and when it was asked, they could not say that it was not lawful.

(b) "Is it lawful" Lk 13:14