Trying to write a brief synopsis of what a Spirit Worker is has turned out to be a lot harder than I thought it would be, but here goes:
Spirit Workers tend to fall into one of the categories below - of course, there are (and always will be) exceptions - this is based on my own personal observations and experience.
Those whom the spirits choose (without any seeming rhyme or reason, sometimes);
Anyone of any religion (or none at all) who feels the presence of, or interacts directly with non-corporeal, intelligent entities (elementals, ghosts or spirits, Fae, guides, angels, etc.);
Those who seek to advance their understanding of, or relationship with, the mysteries of the magical, paranormal or supernatural through training and education.
The first category, those who are chosen, is a tough one. You may think that you aren't an appropriate choice as a "liaison" to the Spirits, or you simply may not want to have been chosen. Yet they keep pulling, poking and prodding. My experience has led me to believe that until you accept their presence in your life, you will find little peace. I've been spirit-whacked upside the head more times than I care to admit, but there it is.
My experiences have also led me to believe that whether you're born with an innate sense, or whether your senses have been heightened through training, doesn't seem to be all that important. You may be naturally psychic/mediumistic, or a Pagan trained to utilize certain methods of contact, or a paranormal investigator using certain technologies to try to facilitate contact. The important part seems to be the active pursuit of understanding or wisdom, and the desire to better oneself, one's life and one's community through spiritual channels - these are the qualities that create the mark of a Spirit Worker on one's soul.
It's a pretty simplistic way to describe something that can be so profound and life-changing, but it's all I've got at the moment. LOL