Mu-sa Ee-sa connection

Sa means energy flowing manifesting itself 

Mu from Musa means source

Ee or I from Isa means all seeing perception

Therefore 

Musa means Source of Universal Energy Manifesting itself, meaning He is the source of all existence!

Isaa means All seeing perception that observes the energy of the Worlds manifesting itself.

Musa creates and is the source while Isaa merely observes and watches him do the Lord's work.