John 16:25 "These things I have spoken to you in figurative language; 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."
Even though the disciples were with our Lord, Who taught and guided them at every opportunity, they could not understand His parables for they did not have the Holy Spirit, Who was given only to the Israelites then.
Luke 8:9 Then His disciples asked Him, saying, "What does this parable mean?"
Mat 21:45 Now when the chief priests and Pharisees heard His parables, they perceived that He was speaking of them. But when they sought to lay hands on Him, they feared the multitudes, because they took Him for a prophet.
The Jews especially the spiritual leaders understood many of His parables for they were the people of God and had the Holy Spirit (until the death of our Lord Jesus). God wanted them to understand so that they would repent and be saved (eg Nicodemus).
Mat 13:34-35 All these things Jesus spoke to the multitude in parables; and without a parable He did not speak to them, that it might be fulfilled which was spoken by the prophet, saying: "I will open My mouth in parables; I will utter things kept secret from the foundation of the world."
Hidden in the parables are the secrets and mysteries of the Kingdom of God. All those without the Holy Spirit will not be able to understand them for God kept the secrets from them.
Secret of the priceless Pearl
Mat13:45-46 "Again, the kingdom of heaven is like a merchant seeking beautiful pearls, who, when he had found one pearl of great price, went and sold all that he had and bought it. "When the merchant finds this priceless pearl, he will sell all he had and buy it."
In this case the priceless pearl is the entrance to the kingdom of heaven or New Jerusalem.
Rev 21:21 The twelve gates were twelve pearls:each individual gate was of one pearl. And the street of the city (New Jerusalem) was pure gold, like transparent glass.
Mat 7:6 "Do not give what is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet, and turn and tear you in pieces."
If non-believer (swine) is able to interpret these few verses, then he must give away everything he owns, in order to be saved or enter the kingdom of heaven (pearl). This is definitely unacceptable to non-believers and he will immediately denounce the word of God as demonic. So all those not saved nor born again (without the indwelling of the Holy Spirit) will not be able to understand the parables of Jesus and His words which have hidden spiritual meanings and teachings concerning the kingdom of God.
But the time is coming when I will no longer speak to you in figurative language
A few hours after these final instructions, our Lord was arrested and then crucified. After His resurrection His disciples were saved and given the Holy Spirit. Only after our Lord was glorified, the believers were filled with the Holy Spirit with the evidence of spiritual gifts but the disciples, who loved Him, were baptized by our Lord with the Holy Spirit or Spirit of truth, Who taught them all things.
John 16:13a "However, when He, the Spirit of truth, has come, He will guide you into all truth;"
Brethren, unless we are baptized with the Holy Spirit by our Lord Jesus Christ (not by man), with the Spirit of truth helping, teaching, guiding us etc. our understanding of the word of God, the parables of Jesus, etc. are limited.