What does Matthew 13:14 mean?

The disciples have asked Jesus why He now teaches the crowds in parables. Likely, they are asking why He doesn't spell out more clearly what He means (Matthew 13:10). From their perspective, it makes sense that if Jesus is more direct, more people will understand and believe. Scripture, in fact, shows this is not the case. Christ's explanation includes a prophecy from Isaiah which dispels that misunderstanding.

Jesus' surprising answer has been that He is teaching in parables, in part, to keep the crowds from fully understanding. These stories are a way of both teaching and restricting full access to the secrets of the kingdom of heaven. That knowledge has been given to the disciples. It is also being kept from the Israelite nation, at large. This is in response to their own stubbornness and disobedience.

This fulfills yet another prophecy from Isaiah. Jesus references the very beginning of Isaiah's work as a prophet of God, described in Isaiah 6:8–10. Isaiah responds "Here I am! Send me," to God's question about who would go for Him. God tells Isaiah to go and tell the people of Israel, in essence, to hear what is told, but not to understand it.

Jesus applies Isaiah's words to this generation of Israelites, as well. He says they will indeed hear but never understand and will indeed see but never perceive. In the case of Jesus' generation, the people have heard the teaching of the Son of God with their ears. They have seen the power of the Son of God on full display in His miracles. But they have failed to understand or perceive that Jesus is, in fact, the Son of God and the Messiah. The ultimate reason for this is rebellion: they don't believe because they don't want to believe (John 5:39–40; 7:17). So, God will obscure their understanding even further, as a form of judgment (Proverbs 29:1).