Complex sentence: However, the voice belonged not to Vercci, but Soul Edge, which assumed his form in Voldo's mind, for while Soul Edge could possess Voldo's heart, it could not change it, for Voldo only serves one master: his beloved Vercci.
Split into simpler sentences: However, the voice belonged not to Vercci, but Soul Edge, which assumed his form in Voldo's mind. While Soul Edge could possess Voldo's heart, it could not change it, for Voldo only serves one master: his beloved Vercci.