: Because
: a) Regret should be dead already.
: - I've never noticed Regret screaming in fear when he's put aside... but it
: that's so (as per the Halopedia transcript) that is an argument that he
: was still "alive".
: b) The dialog.
: - Why would Regret introduce himself? Especially with the word
: "and".
: - I still think the sermon line is off. Why would Regret tell an Oracle to
: stay where he is? He's not a member of the flock.

Regret is so inured in Covenant doctrine that he actually feels that a Holy Ring cannot be activated until he says the magic words. He's that devout and misled. The Monitor quickly corrects him. Presumably the reason Regret was in the lake temple was to perform a sermon. Death is of little concern for the Flood which can reanimate the recently deceased. The Gravemind hauled Regret in the same way as the Chief, most likely. It doesn't need Regret, as it's not a Reclaimer, so it began the assimilation process but it does potentially need the Chief 'to stop the key from turning', so the Chief is left alone.

Regret does in fact scream in fear when he's shoved aside. It was in the original as well. The Gravemind can keep Regret's mind and thoughts intact if it so chooses.

The Monitor, though unable to move about, nevertheless prattles on about containment and protocol as though it's the only thing on its mind. He knows the Flood has to be stopped, but he's just not capable of doing so while captured.