Mundus had intended to make the Underworld and the Human World one by cutting off their barrier.
Maybe this was Mundus's attempt to "impress"/taunt Sparda before his outright rebellion. "Oh you like these humans so much? Allow me to make these worlds one so you can always be by their sides. My gift to you, Sparda, my gallant knight."
Cue Sparda's grief and rebellion
And Sparda "hold no grudges against his own kind", meaning Sparda did what was right. To save the humans.










