Jesus frequently taught in parables. He uses the parables as concrete illustrations of intangible principles. Those who hear the parable and can make the connection between the tangible and the intangible are the ones to whom He is actually speaking.
That sounds exclusive or elitist, like He was speaking in code simply for self-aggrandizement. That is not really the case.
God wants our hearts softened towards Him and towards the people around us. When Jesus quotes the passage from Isaiah, he is quoting from the Septuagint version (please read the footnote in this link). These are the scriptures many of Jesus' hearers would have known.
From the beginning of His teaching ministry, Jesus quoted the Old Testament scriptures that the Jews of that day would have been familiar with. He did this, not because He needed the bolstering of that authority, but because it was the authority His hearers knew. They needed that assurance that His teaching came from the correct source.
When He taught in parables, some people "got it" the first time around. Others had to think about it before they could come to the proper conclusion. Others simply dismissed it as a cute story.
Hmmm... How many times do we come away from church, remembering the preacher's illustration as simply a cute story, forgetting the principle contained therein?
Help us to tune our ears to Your words. Open our eyes to see Your instructions clearly. Soften our hearts toward You that we might turn and repent and be healed.
In Jesus' most precious name.