No, but it can help. Spirituality proceeds along the lines of ideas that you have about it. The ideas flower in your brain and open up new ways to think about things. Having a mentor can jumpstart that process and even kick it into overdrive.
Your mentor does not even have to be a real live person. My mentors included Osho and David Hawkins, and I never met either of these men in person. I just read their books.
Atheists have spiritual lives too, guess what they use for this purpose? Comic books, movies, and science fiction.