Dr. Isaac Levy includes this
explanation in his English translation of Rabbi Samson Refa'el
Hirsch's commentary on Numbers 16:4):
The origin of this meaning is to be found in the work of the
Creation. The visible material world created in six days received
with the seventh day a day of remembrance of, and bond with its
invisible L-rd and Creator, and thereby its completed consummation.
Similarly the symbolism of the number seven in the Menora, in the
Temple, in the Mussaf offerings, in the sprinklings of the blood on
Yom Kippur, in the Festivals of Pesach and Succoth, in Sabbath,
Schmita, Tumma etc. etc. The symbolism of the number eight:
starting afresh on a higher level, an octave higher. The eighth day
for Mila, Schmini Atzereth and Israel as the eighth of G-d's
Creations. With the creation of Israel G-d laid the groundwork for
a fresh, higher mankind and a fresh higher world, for that shamayim
chadashim and the `eretz chadashah for which Israel and its mission
is to be the beginning and instrument (Is. LXV,17).
So that there are three elements in us. (a) our material sensuous
bodies, like the rest of the created visible world = 6; (b) the
breath of free will, invisible, coming from the Invisible One = 7;
(c) the calling of Jew, coming from the historical choice of Israel
Jews entered a covenant to assume a role as a "kingdom of priests".
This priesthood requires reminding the world of the notion of "8", so
that the world can get beyond the physical "6" and reach the
free-willed, created, human, sanctity of "7". Eight is therefore not
above all of creation, but beyond this universe. Eight represents
man's ability to rise to angelic heights -- yes an image of growth,
but not unobtainable. Man connects two worlds, eight connects those
worlds. (Which is why the letter chet, the eighth letter, is drawn in
the Torah as two copies of the seventh, zayin, connected by a bridge.)
Which is why the laws of the covenant G-d made with Noah and thereby
all of humanity are grouped into seven commandments, and the sign of
that covenant is seen in the seven-colored rainbow.
For Rav Samson Rephael Hirsch, the week gives meaning to the numbers
six and seven. The Maharal, though, finds that the week itself is
based on a more primary idea. He attributes the symbolism of six and
seven to the structure of space: When you look closely you will find
that the physical has six opposing sides, which are: top and bottom,
right and left, front and back. All these six sides are related to the
physical, because each side has extent, and limits physical objects.
But, it also has in it a seventh, and this is the middle, which has no
exposure on any side. Because it is not related to any side it is like
the non-physical, which has no extension [takes up no volume of
space]. (Gevuros Hashem 46)
Six, then, is the physical world. Not so much evil as something we need a seventh to harness, and an eight toward which to grow. A tool that will hopefully be used for good, not good or evil in-and-of itself.