'He'. Hu stands for the Essence Itself. It stands for 'He Who is Absent'. Dhikr of 'Hu' is one of the most powerful words of Remembrance. When the lover is annihilated in the Essence Itself, there is no duality, no dhikr of 'Hu' - only Oneness, only the Beloved. When 'He' is no longer absent, who is there to call to? The Principle insofar as It is Itself; the Essence beyond the Qualities. The mystery of Ipseity, of Essentiality, of Aseity.