Why do dream have a huge role in Shakespeare's A Midsummer Night's Dream, and are dreams a negative thing since they take away from the real truth?

The answer to this lies in part in understanding the
historical importance of Midsummer festivals, upon which Shakespeare's A
Midsummer Night's Dream is founded. Midsummer festivals were still a large
event in Elizabethan England, although the pagan festival had been Christianized with an
emphasis on John the Baptist instead of on the Summer
Solstice.

Midsummer festivals
historically celebrated the gods and emblems of the
solstice. Bonfires were set to honor the Sun, at its apex at summer solstice. Maidens
historically went to bed that night with folk magic rituals and charms to bring their
true loves to them. This had symbolic association with the first harvests, especially so
in northern climes with short growing seasons. So, love, magic, dreams, and power (as
from the Sun) were overriding themes at play during Midsummer's night. This gives a
brief historical perspective as to why dreams play such a large part in
Shakespeare's play.

Further understanding
stems from a brief textual analysis. Shakespeare opens the
comedy with dialogue between Theseus and Hippolyta who establish the dream and love
themes. Theseus speaks of their approaching wedding ("our nuptial hour / Draws on
apace") that will be held at the time of the full moon ("four days brings in another
moon"). He then complains that the current moon changes phases too slowly for his
happiness, "she lingers my desires." In these lines, Theseus introduces the idea of love
through his upcoming wedding day and of his delayed "desires." He also introduces the
idea of dreams through the association with the moon--what else does one do when the
moon is on the rise? One sleeps. One dreams.

When Hippolyta
responds, she reinforces both ideas about dreams and love. Her first remarks are that
the days "will quickly steep themselves in night" and that the "nights will quickly
dream away the time." Her closing line gives a feminine expression to the sentiment
Theseus referred to as "desires"; she says the moon shall soon "behold the night / Of
our solemnities." So through her dialogue, Hippolyta confirms the importance of the
themes of dreams and love in the upcoming play.

When you
combine the importance of the themes of love and dreams in the play with the
understanding of the importance of Midsummer festivals, it is easier to see whether
dreams are a negative thing or not, and whether or not this play presents the dreams of
the play as a departure from reality. Since dreams are an important part of Midsummer
festivities, and since the text of the opening lines of the play establish dreams and
love under the Midsummer moon as desired, sought for, and happily anticipated, and since
dreams fit precisely with the reality of the historical activities of Midsummer
festivals, it may be stated that dreams in this comedy are not negative
and are not meant to be seen as a departure from reality--we may have
departed from the reality of ancient celebrations of Midsummer festivities but for
Elizabethans Midsummer festivities were not seen as a departure from
reality.