The Purpose of Parables
In Matthew 13:10–17, Jesus explains to His disciples why He teaches in parables.
This is why I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand. (v. 13)
This passage may appear perplexing at first, especially when Jesus indicates that His actual intention in speaking in parables is that truth would be concealed from those on the outside.
How should we make sense of this? First, Jesus is clearly teaching that the secrets of the kingdom of God are unknowable through mere human reasoning and intuition. Jesus does not say that no one can ever understand the parables or that He intends to hide their truth from all people. Instead, Jesus explains that in order to highlight God's sovereign grace, God in His mercy has enlightened some, to whom "it has been given to know the secrets of the kingdom of heaven" (v. 11, emphasis added), so that they might understand the truths of God's kingdom. Those who have been given knowledge of the secrets of the kingdom will be given "more," while those who have not received such knowledge will eventually have whatever blessings they appear to possess taken away (v. 12). In other words, those who have been given this gift from God will continue to grow in their faith, while those who have not been given the gift will lose everything on the last day.
Second, many hear Jesus' preaching and refuse to believe what He says. These are people who "see" and yet do not truly see, who "hear" and yet do not truly hear (v. 13). They are those who are confronted with the truths of the kingdom of God and who nonetheless stubbornly choose to reject them. Jesus' teaching in parables (which cannot be understood by those without the key of knowledge) is judgment on their unbelief, while at the same time it brings blessing to those who have been taught the parables' meaning. Insofar as unbelievers remain unrepentant, they are cutting themselves off from the grace of God and stand under His judgment. The disciples (and all who would become disciples after them), on the other hand, have been granted eyes to see and ears to hear Jesus; they have been given the secrets of the kingdom (vv. 11, 16). God's mercy has been extended to the disciples who, like many in the crowds, once ignorantly and stubbornly rejected God.