In Matthew 13, the disciples asked this same question of Jesus in verse 10. He answered, “The knowledge of the secrets of heaven has been given to you, but not to them. This is why I speak to them in parables, Though seeing, they do not see; though hearing, they do not hear or understand” (Mat. 13:11,13).
Jesus is not withholding the truth from some; He isn’t saying that only the smart people will understand and be saved. Some people understand spiritual truth and some do not; some have eyes to see and ears to hear, some do not. In the above verses, and through the use of parables, Jesus is making comment on the spiritual condition of people. Through their understanding, or lack thereof, of the teachings of Jesus, we can easily see who has eyes to see and ears to hear the things of God.
When Jesus had the rapt attention of His audience and the people were humble and anxious to hear, Jesus spoke plainly. But, when His audience contained people who were prideful and resistant to His instruction, He used parables that pierced the hearts of those who were open but were lost on the proud.
Second Peter 3:9 teaches that God does not want anyone to perish but, rather, that all would come to repentance. His desire is that all people would turn to Him and seek understanding of the truths of His Word. He promises that if a person seeks after God, He will reveal himself.