The SHIELD is associated with Avraham Avinu because HE went into the fiery furnace, because HE went to war against the Four Kings. Because Avraham did not hesitate to risk his life to be a light to the nations, as H” requires, therefore did H” provide His impenetrable Shield.
Black Fire on White Fire 
The SHIELD is associated with Avraham Avinu because HE went into the fiery furnace, because HE went to war against the Four Kings. Because Avraham did not hesitate to risk his life to be a light to the nations, as H” requires, therefore did H” provide His impenetrable Shield.
Even more clear is that the Almighty tells Avram, “I am your shield” (Gen. 15:1).