Servant Attack = Has mystery, can affect spiritual bodies, has magical energy
Normal punch is a normal punch.
A Servant attack cannot affect a human's spirit or soul.
The soul is on another plane of existence and requires a conceptual weapon to affect.
The spirit is attached to the body.
However, if you were able to do something that separated your spirit from your body a Servant can hurt that. A Servant can also eat your spirit/mind and your soul.
A Servant attack will do nothing to your mind or your soul as long as the attack is not conceptual.
Basically, a Servant is a ghost that can hurt both ghosts and people.