Why does the nurse stand lamenting in the first scene of Medea?

In Medea, the nurse stands lamenting as a way to set the tone of the play and to introduce the situation to the audience.  The nurse recounts the events that have happened before the immediate scene of the play so that the audience understands the grievances that Medea has against Jason.  The nurse's lament does seem to "ask" for the audience's sympathy towards Medea's situation.  At the end of the lament, the nurse fears what Medea might do to set her course straight, and with this comes the tone of suspense as the audience becomes expectant and also tries to foresee how Medea will handle this situation.