Read Descartes, Meditations 1 and 2. What is the significance of the wake/sleep contrast in these two meditations?

Descartes' wake/sleep contrast is central to his famous Dream Argument, whereby he is can find no conceivable way to differentiate between whether he is either dreaming or awake in their perceptions of the environment. As Descartes states in his Meditation 1:
"…and to experiencing in my dreams the very same things, or now and then even less plausible ones, as these insane people do when they are awake. How often does my evening slumber persuade me of such ordinary things as these: that I am here, clothed in my dressing gown, seated next to the fireplace--when in fact I am lying…