The role of Jacques in this excellent comedy seems to be as a character who is separate and distant to the rest of the characters. He alone is the one character who is not transformed by the magic of the Forest of Arden, and he comments critically and the duplicity of other characters, seeing through Touchstone's supposed marriage to Audrey, recognising that it is more about lust than it ever is about love.
Perhaps the best speech we can use to answer this question, however, is the famous speech about the "Seven Ages of Man." What is key to realise is that in this speech, the "lover, / Sighing like furnace, with woeful ballad / Made to his mistress' eyebrow" is just another role played by another player that comes and then goes. There is nothing of lasting value in any of these roles because they are all temporary. He has nothing to stay that is good or beneficial about these separate stages, as the sarcasm in the lover role displays. Jacques therefore in his character expresses a pessimism that acts as a kind of antidote to the other characters and the way that they are overwhelmed by love and are transformed by the Forest of Arden. Lastly, it is key to note that he does not play any role in the marriage celebrations that end the play. Love is something that he sees no purpose in, as it is just another stage of many that man goes through.