Matthew 13:13-14, 35

This is the reason I speak to the crowds in parables: because while [having the power of] seeing they do not see, and while [having the power of] hearing they do not hear, nor do they understand and grasp [spiritual things]. In them the prophecy of Isaiah is being fulfilled, which says, ‘YOU WILL HEAR and KEEP ON HEARING, BUT NEVER UNDERSTAND; AND YOU WILL LOOK and KEEP ON LOOKING, BUT NEVER COMPREHEND

This was to fulfill what was spoken by the prophet: “I WILL OPEN MY MOUTH IN PARABLES; I WILL UTTER THINGS [unknown and unattainable] THAT HAVE BEEN HIDDEN [from mankind] SINCE THE FOUNDATION OF THE WORLD.” [Ps 78:2]