What is the meaning of the Star of David? What I mean is where does it come from and why does it have six sides? It is often represented with the two triangles. Does this have any significance? Is it related to the pentegram? Why did David use it?

Answer

Through our long and often difficult history, we have come to the realization that our only hope is to place our trust in God. The Magen David (literally "Shield of David") has six-points, which symbolize that God rules over the universe and protects us from all six directions: North, South, East, West, Up and Down. A similar symbolism is found in reading the "Shema." ("Code of Jewish Law" O.C. 61:6)

Thus, King David used this six-pointed symbol to signify that the Almighty shields him in war. (Rabbi Moshe Feinstein - "Igrot Moshe" O.C. 3:15) 

A more practical theory is that during the Bar Kochba rebellion (1st century), a new technology was developed for shields, which used the inherent stability of the triangle. Behind the shield were two interlocking triangles, forming a hexagonal pattern of support points. If you've ever seen a Buckminster Fuller geodesic, you know how strong triangle-based designs are!

A cynical suggestion is that it is an appropriate symbol for the internal strife that often afflicts Jewish nation: two triangles pointing in opposite directions!

In Kabbalah, the two triangles represent the dichotomies inherent in man: good vs. evil, spiritual vs. physical, etc. The two triangles may also represent the reciprocal relationship between the Jewish people and God. The triangle pointing up symbolizes our good deeds, which go up to heaven and activate a flow of goodness back down to the world, symbolized by the triangle pointing down. 

Another idea is that a cube, which has six sides, receives form and substance from its solid center. This inner core represents the spiritual dimension, surrounded by the six universal directions. So too, we see this pattern in the six-pointed star with it's hexagonal center. By the way, the same idea applies to Shabbat -- the seventh day which gives balance and perspective to the six weekdays.

As for the yellow, presumably this is an invention of the Nazis, who forced Jews to wear yellow stars so that they could be recognized from afar.

So whether it is a blue star waving proudly on a flag, or a yellow star in a concentration camp, the Star of David stands as a reminder that for the Jewish people... in God we trust.