The first interesting point Tasker makes here is that, if you follow the narrative of Matthew, Jesus at one point makes a conscious decision to move from simple illustrations to the use of parables. And this transition was clear enough (i.e. enough of a change from his previous preaching) that the disciples noticed it and were curious enough to ask about it.

The text in question is:

Matthew 13:10 Then the disciples came and said to him, “Why do you speak to them in parables?” 11 And he answered them, “To you it has been given to know the secrets of the kingdom of heaven, but to them it has not been given. 12 For to the one who has, more will be given, and he will have an abundance, but from the one who has not, even what he has will be taken away. 13 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.

Tasker comments:

Perhaps the most important and distinctive feature of this chapter is that the evangelist, by the words of Jesus that he records in verses 10-15, makes it clear, as the other evangelists do not, that Jesus deliberately adopted the parabolic method of teaching at a particular stage in His ministry for the purpose of withholding further truth about Himself and the kingdom of heaven from the crowds, who had proved themselves to be deaf to His claims and irresponsive to His demands. Hitherto, He had used parables as illustrations, whose meaning was self-evident from the context in which they were spoken (e.g. vi. 24-27). From now onwards, when addressing the believing multitude he speaks only in parables (34), which He interprets to His disciples in private. Matthew alone tells us that the disciples, apparently surprised at this new development in His policy, asked Him Why speakest thou unto them in parables? The answer they received was that there were mysteries of the kingdom of heaven which could not be understood by those who, He said, using language similar to that used by Isaiah about his contemporaries (see Is. vi. 9, 10), looked upon Him with their eyes but never understood the significance of His Person, and heard His teaching with their ears but remained deaf to its implications. When such people heard a parable about the kingdom it would therefore be for them an interesting but pointless story conveying no revelation of divine truth. The disciples, on the other hand, had already grasped something of the supernatural character of their Master and of the kingdom He came to inaugurate…in their case there was another illustration of the proverbial truth that whosoever hath, to him shall be given, and he shall have more abundance…

– R.V.G. Tasker, Tyndale New Testament Commentary: The Gospel According to St. Matthew, pp. 134-135

Another interesting point is his comment on “whosoever hath, to him shall be given…,” which implies that the spiritually-minded have discernment to perceive truth in places that others will see as nothing but an interesting story.