Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
What is the basis of the dhikr ‘Hu’?
Dhikr or remembrance means for the One being remembered to be present in the heart of the one remembering Him. ‘Hu’, meaning ‘Him,’ is a pronoun which refers to Allah the Creator. If your heart is present with the One being remembered while you are repeating the word ‘Hu’, then you have attained the purpose of the dhikr.