I think that the theme of this chapter is best explained by verse 22
22 And no man putteth new wine into old bottles: else the new wine doth burst the bottles, and the wine is spilled, and the bottles will be marred: but new wine must be put into new bottles.
Jesus is talking about how the Law of Moses is fulfilled with his mortal ministry. He makes the analogy between the old covenant and the new covenant like putting new wine into new bottles. Basically, he's saying that the old things are done away in Him and that there is a new law and a new covenant. In other words, the old law can be done away with completely as the new law completely takes its place.
This can be applied to our lives as we put off our old ways and start anew by living the more up-to-date law.
The literary form is a narrative, but it also employs anecdotes and the cited analogy in order to teach a principle.
Mark Chapter 2 is a narrative. The theme is Jesus' role here on earth and the role of people as his followers. Jesus performs miracles and does things that the Jews thought were against the laws. However, he is showing that if we live in him, that he is Lord of all and that he is the laws.