Albert Barnes on Matthew 11:15

He that hath ears, etc. This expression is frequently used by Christ. It is a proverbial expression, implying that the highest attention should be given to what was spoken. The doctrine about John he regarded as of the greatest importance. He among you, says he, that has the faculty of understanding this, or that will believe that this is the Elijah spoken of, let him attend to it, and remember it.

(n) "He that hath" Rev 2:7