What does Matthew 13:35 mean?

Matthew has repeated once more in this chapter that Jesus spoke to the crowds only in parables (Matthew 13:3, 34). Parables are short stories or illustrations designed to reveal a larger truth. Jesus most often used them to describe the kingdom of heaven. The parables were often hard to understand, and Jesus described them in greater detail to His disciples. Previously, it seemed that Jesus was more direct, as in the Sermon on the Mount (Matthew 5—7). The shift to a more obscure style is probably what prompted the disciples to ask this question. Jesus responded that it was because of the hardness of the people's hearts (Matthew 13:15). They refused to believe, so in a form of judgment, they would be made even more resistant.

In that passage, Jesus made it clear that this fulfilled a prophecy of Isaiah (Matthew 13:14). Now Matthew points to Jesus' use of parables as the fulfillment of yet another prophecy, this one from Psalm 78:2: "I will open my mouth with a parable; I will utter dark sayings from of old." Matthew's version of the text changes the last line to "what has been hidden since the foundation of the world."

Matthew applies Asaph's words from Psalm 78 to Jesus. In doing so, he describes Jesus' parables as revelations of long-hidden truths about the nature of the kingdom of heaven. By communicating those truths in the form of parables, they remained hidden for many of Jesus' listeners.