What does Matthew 13:12 mean?
Jesus is preaching to a huge crowd of Israelites. He is teaching them in parables: small stories used to illustrate truths about the kingdom of heaven (Matthew 13:1–3). The disciples come to Him and ask why He teaches the people this way (Matthew 13:10). Likely, they are asking why He is not more straightforward about what He means, as He was during the Sermon on the Mount (Matthew 5—7). Jesus has told them that the secrets of the kingdom of heaven have been given to them and not to the people (Matthew 13:11).Now He adds that more will be given to the one who has, but from the person who does not have, even more will be taken away. In this context, what is given and taken is knowledge about the kingdom of heaven. By extension, this also implies the ability to participate in the kingdom. In the arrangement of Matthew's gospel, this follows Christ's statements in the previous chapter about the coming judgment for "this generation" of Israelites. This was due to their lack of repentance and rejection of Him as the Messiah.
The disciples' commitment to Jesus as the Messiah results in them being given more and more understanding about the coming kingdom of heaven. Israel's rejection of the Messiah, as a nation, has resulted—and will result—in being given less and less understanding. Much as with God's approach to Pharaoh in the Exodus (Exodus 4:21; 8:32; 14:4), those who resist God will have their hard-headedness amplified, as a judgment of their disbelief.