10 As soon as He was alone, His followers, along with the twelve, began asking Him about the parables. 11 And He was saying to them, “To you has been given the mystery of the kingdom of God, but those who are outside get everything in parables, 12 so that while seeing, they may see and not perceive, and while hearing, they may hear and not understand, otherwise they might return and be forgiven.” (Mark 4:10-12 NASB95)
This text sits awkwardly in its present context. The previous context is about Jesus teaching the crowd in a boat (4:1-2). Without further explanation, Mark shifts the narrative that takes place in private with those around his Twelve disciples (4:10-12), a small group of disciples. Another textual issue that occurs in the passage is the use of plural form of parables, whereas Jesus completes one parable (4:3-9). The placement of the discourse between Jesus and “those around him” also interrupts the sequence of parable. Jesus was still on the boat in the sea (4:1-2), but he and “those around him” appear to be in a private (4:10-12) and the clarification of the parable occurs again in the boat in the sea (4:35-36). At this point, Jesus is again in the public setting with his disciples in the boat. With few exceptions, some scholars believed this passage to be a latter insertion. But this inconsistency is more likely due to tradition, so he decided to leave the setting the way it is now.
Many ascribed the Markan redaction to traditional material. One cannot avoid the questions no matter whether Mark inserted his independent tradition unit or borrowed from the tradition within the parable collection. If he borrowed it from Pre-Markan tradition, where did he find it and what qualified him to apply this text there (4:10-12)? His form, materials within his redaction, and context show that he found it in tradition. Yet there are some questions to be asked. Why did Mark quote Isaiah 6 here? Is the text is about double predestination that only elect or insiders are foreordained to hear the message while outsiders’ ears divinely closed? Some people think that v. 7:17 supports it. But what do we do with 12:12 when outsiders also knew that the parable was about them? As Robert A. Guelich asserts that the text is not about the “double predestination” but about the hardness of heart of those who constantly rejected Jesus and his message.
 Guelich, Robert A. Mark 1–8:26. Vol. 34A. Word Biblical Commentary. Dallas: Word, Incorporated, 1998.