For they will not hearken unto me, etc. The words are, as it were, an a fortiori argument. Those who had despised the voice of Jehovah, speaking in his Law, or directly to the hearts of his people, were not likely to listen with a willing ear to his messenger.
We are reminded of our Lord's words to his disciples in Matthew 10:24, Matthew 10:25. Impudent and hard-hearted; literally (the word is not the same as in Ezekiel 2:4), in Revised Version, of an hard forehead and of a stiff heart.
The word "hard" is the same word as the first half of Ezekiel's name, and is probably used with reference to it as in the next verse.