Bungie has a huge "thing" for the number 7. Looking at Halo you have John 117, and 7 squared is 343 Guilty Spark. They use things with 7 throughout most of there games. Its just something you see with Bungie but why they use it so much, is one of those wierd spooky mysterys we'll probably never get told unless we break into the depths of the Bungie vaults :P As for the 7th Column its Bungies elite bunch of insane followers (us basically) who are here to assist Bungie in there conquest of the world and stick the number 7 onto everything. Best thing to do is search for some of the old threads about 7, theres hundreds of pages on theorys and such that your brain will probably explode by the end of it :P