why Jesus spoke in parables....

Let it BE.  Submit to the Will of God...the Author of everything below and above.
Matthew 9:29, Jesus: Let it happen.  Let it happen according to your Faith or unbelief.  Doubt.
Jesus: Pray THIS: the Will of God BE DONE, Divine Will...NOT the human will.

ONE WITH God...ONE WITH His Will, His Truth, Spirit.  God does not lie or make promises He cannot keep.  As...according to that which a man THINKeth...so he IS.

The thief thinks of stealing, the adulterer thinks of adultery.  The carnal minded man is not OF God born.

The priests in the Temple, on Sabbath, break the Law of Moses, and yet they are not GUILTY, Matthew 12:5...when they eat the man-made bread offered to God.   God's SABBATH is to do Good, what is Right...Saves life,   God's Spirit of Love...is Law....Mark 3:4.  Micah 6:8, God has revealed to you WHAT is Good,  THIS...IS what God REQUIRES OF you: to do what is Right, Love Mercy and Walk humbly under, according to the Spirit.

Jesus Spoke in PARABLES...to those who weren't Chosen, Elect.  Jesus spoke in parables to the children of HUMAN fathers.  BECAUSE God had closed their eyes and ears and they were dead SOULS being void of the Spirit, TRUE Life...according to God.  The Chosen, Elect MUST become Born Again by believing...having Faith in God's Revealed Mystery of SPIRITUAL Rebirth, Resurrection of DEAD SOUL asleep in the dream...TEMPORARY life according to flesh.  Those who God SENDS His Spirit into Rise and WALK in His Spirit of Truth.  The Divine Spirit of Power Transforms the sinner into a saint.  His Children Recognize the Truth, embrace God's Truth, become ONE WITH Him and are able to please God instead of FLESH...PHIL 2:10-13.

AS you have believed in God the Spirit, His Word...Truth...PROMISE...SO shall you BE.
Think, Speak...ACT according to Spirit.   You must think...believe...speak the Truth.  Without Faith you will not ever Walk according to, UNDER the Spirit-influence, Power.

The Mystery will never be grasped by the children born of HUMAN fathers, flesh.
HUMAN nature of the human father...is Sin nature....evil.  As many as God HAS Chosen, as many as Chosen TO believe...these will RECEIVE...and Rise from their slumber, death in Sin.

The Parables ARE Spiritual and cannot be understood by  the carnal-minded children of THIS world below...not without the entrance of the Spirit into the SOUL to cast out darkness, unbelief,doubt.
Yes...Greater IS He...within us.