The Star of David is allied with Jewish mysticism and still holds to the original representation of the star tetrahedron also known as the Merkaba.
The upward pointing star represents the sun, fire and masculine energy. The downward pointing star represents the moon, water and feminine energy. As always, when the symbol is placed within a circle we see the trinity.
In the Kabbalistic tradition the hexagon symbolizes the six directions of space, the divine union of male and female and the four elements.