Jamieson, Fausset and Brown on Ezekiel 3:27

27. when I speak ... I will open thy mouth--opposed to the silence imposed on the prophet, to punish the people (Eze 3:26). After the interval of silence has awakened their attention to the cause of it, namely, their sins, they may then hearken to the prophecies which they would not do before.

He that heareth, let him hear ... forbear--that is, thou hast done thy part, whether they hear or forbear. He who shall forbear to hear, it shall be at his own peril; he who hears, it shall be to his own eternal good (compare Re 22:11).