Symbolically Spiritual truth that is available to us at any particular stage of understanding is often shown to us as though in a reflection. It is as if we need an image that gives us tangibility.
Psychological / Emotional Perspective:
Often, to see a reflection in a dream is to try to be understanding the inner self and the way that we cope with the outside world. If in a dream the two images do not correspond, we will need to make some kind of adjustment in order to live comfortably within the everyday world. Our inner self must give the impetus to the outer reality.
Everyday Material Aspects:
A reflection seen in a dream has a great deal to do with the way we see ourselves at that particular moment. Our self-image is important to us, as is the way other people see us. If the reflection is in a mirror, then our image will be perhaps more ‘solid’, whereas one seen in water will be more transient. The story of Narcissus and the way he fell in love with himself (or rather his own image) is a warning to all of us against self-worship.
You might also like to consult the entry for Mirror.