The 343 Guilty spark called the Master Chief a reclaimer because Humans in general are all reclaimers, not only are they reclaimers of the index when the flood get out of control (as of course, they knew would just because they knew that humans would survive and inevitably stumble upon the halos and release the flood) they are also reclaimers of the forerunner technology.
This would support the Audio Recording:
"Perhaps through others eyes you may find how to save us all"
that is obviously a forerunner leaving one final order for the monitor for when the humans (whom they have influenced on purpose to eventually try and solve the flood problem)