Matthew 13:10-17 (KJV)
And the disciples came, and said unto him, Why speakest thou unto them in parables?
He answered and said unto them, Because it is given unto you to know the mysteries of the kingdom of heaven, but to them it is not given.
For whosoever hath, to him shall be given, and he shall have more abundance: but whosoever hath not, from him shall be taken away even that he hath.
Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand.
And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive:
For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.
But blessed are your eyes, for they see: and your ears, for they hear.
For verily I say unto you, That many prophets and righteous men have desired to see those things which ye see, and have not seen them; and to hear those things which ye hear, and have not heard them.
After the Pharisees had been given several warnings regarding their unbelief, Yeshua began a series of teachings on the mysteries of the Kingdom of Heaven. This time, however, He spoke only in parables when He addressed the multitudes. This apparently confused the disciples and they came to Him to inquire about His reasoning for this manner of teaching (verse 10). Quite plainly Yeshua explained that the mysteries of the Kingdom were given to the disciples and not to the multitudes (verse 11). He then quoted from Isaiah 6:9,10 for His answer (verses 14 and 15).
Isaiah 6:9-10 (KJV)
And he said, Go, and tell this people, Hear ye indeed, but understand not; and see ye indeed, but perceive not.
Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed.
It is obvious that Yeshua had begun to hide His message regarding the mysteries of the Kingdom of Heaven so that the multitudes, which included His opponents, would not understand what He was teaching. Yet, Yeshua said that the disciples' eyes and ears were blessed because they would be able to understand (verse 16).
Yeshua's hiding of His teaching was in no way an obstacle to anyone who seriously was searching for the truth of God. The principle expressed here relates how those who are open to the message of God will hear and understand, but those who are not open will not hear nor understand. Yeshua also seemed to be applying the "pearls before swine" advice.
Matthew 7:6 (KJV)
Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you.
The Pharisees had been given multiple opportunities to hear Yeshua and to repent, but most refused. Why should they be given any further pearls? The mysteries of the Kingdom of Heaven would be given to those open to repentance and faith.