What is it we mean when we say "in spirit"? It is grounded in a belief that we continue living after our death, but not in a human body. We linger in the ether, we are sensed and can influence, like the wind, like a breath.
In Hawaii, it's a permeating part of their culture to take consideration of their ancestors and be receptive to any nudges through spirit. However not easy, since it's scary to feel the presence of a passed on loved one, since we're then reminded of our own death too. Whenever I have, I understand it as a warning.
It's a mystery!