the cov. think that halo is of immense religious significance. we already know that the cov. use the same symbols as the for. why is this? given that they are a religious army, it makes sense that the best fighters would adorn themselves with religious symbols. religious symbols tend to have been around forever, just look at our own, they predate our entire "advanced" culture. here's my theory.
the forerunners were a widely travelled bunch in their time, they may have deliberately or accidentally left items on many worlds. any early pre-technology cov. races finding these items would take them to be magical or mystical.
"any sufficiently advanced technology is indistinguishable from magic" - Arthur C. Clarke
so these symbols become part of early cov. religion. fast forward, the cov. races explore space. they encounter eachother and what do you know, they share symbols in their religions. this is the glue that binds the races. on their travels they find other examples of forerunner artifacts. they develop aspects of their own technology by reverse engineering forerunner artifacts.
so halo, whether it was found by the covenent before the game starts or whether it was as a result of cortana's "blind" jump, is the ultimate artifact. a complete functioning world full of the technology that has got the cov. where they are today. no wonder they want to access the restricted areas.
This has been theorized before, but it's wrapped up nicely (if still lacking in capitals...).