The Oracle Speaketh! Is this a corallary to M's the Abathya Abetya?, (someone help me here, "the unmanifest sutra")
"Amma has advised us to chant "Om" before and after meditation because this helps to "fence" and hold the energy that is created during meditation. It is like putting walls up on both side of a river. When the river grows due to heavy rainfall, its waters will be contained and channeled instead of spreading across the land and leaking away."