Mat 13:10 -11,13 And the disciples came and said to Him, "Why do You speak to them in parables?" He answered and said to them, because it has been given to you to know the mysteries of the kingdom of heaven, but to them it has not been given... Therefore I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand."
It was God's will that all Jesus' disciples must understand truth or the mysteries of the kingdom of heaven hidden in the parables. Until then, our Lord had to explain each parable to them.
Mark 4:33-34 And with many such parables He spoke the word to them as they were able to hear it. But without a parable He did not speak to them. And when they were alone, He explained all things to His disciples.
Mat 21:45 Now when the chief priests and Pharisees heard His parables, they perceived that He was speaking of them. (Read Mat 21:33-46)
Our Lord Jesus ensured that all hearers understand their sins they were committing, though they may not understand the hidden mysteries. Similarly, whenever we read the bible, and if His words, teachings or parables convict us, thank God that He is leading us into His truth once we repent.
John 6:66-67 From that time many of His disciples went back and walked with Him no more. Then Jesus said to the twelve, "Do you also want to go away?"
Thousands followed Jesus for they saw His many miracles (thousands fed, blind could see, dead resurrected, walking on water, etc.). But when His teachings were difficult to accept, many of His disciples left Him except for the few faithful disciples.
John 6:68-69 But Simon Peter answered Him, "Lord, to whom shall we go? You have the words of eternal life. Also we have come to believe and know that You are the Christ, the Son of the living God."
John 16:25-27 "These things I have spoken to you in figurative language (teachings, parables, words, etc.); but the time is coming when I will no longer speak to you in figurative language, but I will tell you plainly about the Father. In that day you will ask in My name, and I do not say to you that I shall pray the Father for you; for the Father Himself loves you, because you have loved Me, and have believed that I came forth from God."
Finally, after about 3 years, our Lord found that His disciples loved Him for they had obeyed His words resulting to them understanding the mysteries hidden in His words, teachings and parables.
John 16:29-30 His disciples said to Him, "See, now You are speaking plainly, and using no figure of speech! Now we are sure that You know all things, and have no need that anyone should question You. By this we believe that You came forth from God.”
It was music to His ears to hear His disciples saying these words. His subsequence sufferings and crucifixion were pure joy for He had accomplished His most difficult task of transforming His disciples.
John 16:31-32 Jesus answered them, “Do you now believe? Indeed the hour is coming, yes, has now come, that you will be scattered, each to his own, and will leave Me alone. And yet I am not alone, because the Father is with Me.”
Brethren, what great joy it will bring to God, when we too can know the truth by understanding the hidden mysteries of the Kingdom of heaven within His words, teachings and parables.