Reversed messages

Summary

In the cutscene before The Arbiter, you hear a mysterious voice chanting. If this mumbling is reversed (listen), a voice is heard saying:

...I have walked among men and angels for three thousand years. Time has no end... no beginning... no purpose.

I wander the earth, seeking forgiveness for my horrible crimes against God and man.

I live to see death, destruction, over the light, but the light cannot be extinguished.

I live in a prison of my own demise.

I am lost in time...

The voice is speculated to be Gravemind, however, this is up to debate. The voice is also heard during the level Gravemind when you rescue the Marines, and during The Great Journey when you fight Tartarus.