Why did Shakespeare add the characters of Touchstone, Jaques and Audrey to As You Like It and how can they be seen as both important and unimportant?
These characters all serve a purpose in the play and it would be difficult to imagine As You Like It without them. Jacques is a melancholy philosopher, a character type who is often seen in Shakespeare's comedies, who lends an air of cynicism and stark reality to situations that might otherwise be romanticized. Jacques has been living in the Forest of Arden in exile with the Duke, and so serves as a kind of guide to life in the forest when the visitors from court arrive.
Touchstone, the court's "fool" who accompanies Rosalind and Celia on their journey to the Forest of Arden, adds a comic flair, with his efforts to find the humor in every situation. He is knowledgeable of the ways of the court, which he takes pleasure in being part of, but also mocks it when the occasion suits him. Still, he finds the forest and its rural inhabitants charming, and he woos the country wench Audrey.
Audrey is uneducated and claims to not understand many of the words Touchstone uses, but she serves as a character who reminds us of the simple pleasures of life in nature, and provides a sort of bridge between the worlds of the court and the forest. Her decision to marry Touchstone and return to court with him is symbolic of the influence that the ways of the forest have had on the travelers who spend time there, and its lasting impact upon their lives.
The idea that these characters might be "unimportant" lies in the fact that they are relatively minor characters. However, in many of Shakespeare's plays, minor characters are some of the most memorable ones, and often say remarkable things or inspire curiosity. Sometimes they are even the subject of their own stories, as when Tom Stoppard wrote the play Rosencrantz and Guildenstern are Dead, which imagines what takes place in the world of these very minor characters in Hamlet). Sometimes minor characters have memorable speeches; think of Mercutio babbling about Queen Mab in Romeo and Juliet. Jacques' "seven ages of man" soliloquy in this play is one of the most famous passages in all of Shakespeare's work.