The Covenant has this profecy that those who believe in the great journey, will be spare from the halo's blast (they will not) everyone left will not be spared,(the non-believer, flood, ...)
Correct me if im wrong but I dont think that the prohets even grasp what exactly the halo rings do because they believe it will open a portal of sorts to what they consider the afterlife where they will meet the forunners.
