He (Jesus) answered and said unto them, Because it is given unto you (Believers) to know the mysteries of the kingdom of heaven, (The truth regarding God and his Kingdom) but to them (Unbelievers) it is not given. For whosoever hath, (Faith of the believers) to him shall be given, (The Holy Spirit teaches believers the truth and mysteries) and he shall have more abundance: (For ever learning the truth) but whosoever hath not, (Unbelievers) from him shall be taken away (Satan takes the truth from Unbelievers) even that he hath. (any truth that is told to unbelievers is removed. Matthew 13:11 - 12. 

Therefore speak I (Jesus) to them in parables: because they (Unbelievers) seeing see not; and hearing they hear not, neither do they understand. (The truth) And in them (Unbelievers) is fulfilled the prophecy of Esaias, (A prophecy that is still being fulfilled, confirming Jesus was who he claimed to be).  which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive 

(It is not possible for unbelievers to understand the truth, unless they open their hearts.) 

For this people's heart is waxed gross, (Closed hearts) 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, (Seek, Believe, Repent to Jesus and be Saved) and I should heal them. (And Jesus will open Unbelievers ears and eyes so they will see and understand the truth) Matthew 13:13 - 16 (King James Version)