The Sefer Yetzirah (Book of Creation) teaches the mysteries of the Twenty-two Hebrew letters. The alphabet is presented there as three groups of letters. One group is called the Three Mothers. The second group is called the Seven Doubles. The third group is called the Twelve Elementals. This picture shows how these numbers are also prominent in simple geometry.
From Sefer Yetzirah: Seven – three opposite three, and one is the rule deciding between them.
In terms of colors, ‘three’ are the three primary colors – blue, red and yellow. The ‘opposite three’ are their complements – orange, green and purple. Look at the seven circles here. The circle in the center is brown. This is the seventh – called the Holy Palace (see my picture The Holy Palace).
From Sefer Yetzirah: Seven Doubles in Space are Up and Down, East and West, North and South and the Holy Palace precisely in the center and it carries them all.
Notice how you can see this image as a three-dimensional cube. I got this motif from the artist M. C. Escher. You can see the center point as either going in or coming out – or both. If you focus your eyes on the center point, relax them and breathe, a cube can be seen. A cube has twelve edges. These are the lines that connect the seven circles. The six triangles that are outside of the hexagon/cube complete a Star of David.
– Star of David Cube, Kosmic-kabbalah.com