I just looked up the meaning of butterflies:
Butterflies are also popularly thought to symbolize a person's essence, or soul, either past, present or future.
More on sightings of butterflies and cardinals:
Visits from the Other Side
When deceased loved ones want you to know that they’re around, they might send messengers from the animal kingdom: small, brightly-colored bugs, birds, and butterflies are not an uncommon choice. Things with wings tend to get our attention, and if you allow yourself to tune in, you might even know who has sent them. Their message could be a simple acknowledgment that your loved ones are always around. And if you’re asking the Universe for guidance, seeing a cardinal tells you that Spirit is hearing you and guiding you too.