The meaning here is that the Lord had given both Isaiah and Jesus Christ specific callings by speaking to them, thereby opening their ears. After receiving their callings from the Lord they had the option to reject or accept their responsibilities. Like Jonah, they could have run away, but both chose to be obedient and not turn their back on the Lord.
Isaiah's imagery is appropriate for us as well. We are all born in a carnal world, essentially spiritually deaf. For worldly people have hard hearts, 'and their ears are dull of hearing' (Acts 28:26). In order to hear the things of the Spirit, we must be humble and obedient. When we are, the Lord literally opens our ears to the truth. Hence, Jesus repeatedly exhorted his listeners, saying, 'He that hath ears to hear, let him hear' (Matt 11:15). When this process is complete, we can declare as did Isaiah, 'The Lord God hath opened mine ear (to the things of the Spirit), and I was not rebellious.'