What is the importance of Falstaff in the play? What is Shakespeare aiming at?

Falstaff is one of the play's three foils for Hal. As Hal decides who he is going to be as an adult, he has three options to choose from: his dour father, the rash Hotspur, and the jovial but cowardly knight. In the plays that follow—Henry the Fourth Part Two and Henry V—he becomes more like a combination of his father and Hotspur, a brave warrior who manipulates people with words. But he also acquires some of Falstaff's capacity to understand and communicate with the common man.
Of course, Falstaff and his fellow tavern characters also provide comic relief to the play's story of political intrigue and rebellion. However, if we see the "Henry plays" as the story of Hal's rise to become Henry V, Falstaff takes on his most important role as a possible model for Hal's future: one that he rejects, in the end, but also learns from.