We all know that a six pointed star is called a Magen Dovid. The word Magen means Shield. The Magen Dovid is to remind us how G-d was a Shield for Dovid. The six points represent the six directions that G-d protected him: in the four directions (north, east, west, and south) and up and down. On all six sides, G-d is a Magen, Shield.

In the first paragraph of the Shemone Esray, we say that G-d is a Magen for us. When we say this word, we should remember that G-d is constantly protecting us on all sides from all dangers.