Among numerous other things, it is symbolic of the sun and the seven planets. It is the Star of David, a symbol of Judaism, found on the flag of Israel.
Astrology's cornerstone, "As Above, So Below" is portrayed within the Hexagram.
"The Hexagram is the Signet Star of the Macrocosm or Greater World, therefore is it to be employed in all invocations of the Forces of the Sephiroth: though the Signet Star of the Pentagram represents their operation in the Luna World, in the Elements and in Man." (Golden Dawn, Hexagram Ritual)
Kether: MACROPROSOPUS; The Vast Countenance; The Ancient of Days... Kether emanates first as ABBA [of YOD], the Supernal Father, and AIMA [of HEH] the Supernal Mother. ELOHIM is the name given to these two persons united. ELOHIM is the parents of THE SON ZAUIR ANPIN, or MICROPROSOPUS.
"The Hexagram is a powerful symbol representing the operation of the Seven Planets under the presidency of the Sephiroth, and of the letters of the seven-lettered Name, Ararita: Ararita is a divine name of Seven letters formed of the Hebrew initials of the sentence: 'One is his beginning. One is his individuality. His permutation is one.'" (Hexagram Ritual)