: I don't remember the exact quote, but in Halo 1 during the library level as
: you're fighting with wave after wave of flood, 343 Guilty Spark keeps
: talking about various aspects of the flood, its containment and storage on
: the ring, and your armor and weaponry. I remember him commenting about how
: they were kept on the ring for study. The Covenant are referred to by him
: as meddlers as well, as they are the ones who let the flood out on
: installation 04.

: Also, in the Forerunner trilogy of books, humanity was seen as having had a
: method of dealing with the flood. The Forerunners thought that humanity
: had once defeated the flood and driven them back, only to be defeated by
: the Forerunners and de-evolved into primative life forms. It's unclear if
: humanity actually did defeat the flood in the books, but that was the
: going theory as far as the Forerunners thought of humanity. They
: designated humanity to be reclaimers on the chance that humanity would one
: day be able to defeat the flood again, since the Forerunners were never
: able to defeat the flood themselves. They kept the flood on the rings
: hoping to one day come up with a method of defeating the flood as a
: back-up plan, I think.

Problem with that theory is the Primordial goads the IsoDidact that the humans didn't find a solution for the Flood--they chose deliberately to withdraw, to test humanity later.

We don't actually know if that's true or not, but the IsoDidact certainly acted like it was.