a) A the-ist implies ones consent to a suggested the-ism...that's the foundation of religion/religio - "to bind anew".

b) Gnostic/gnōstos/gno - "to know" implies ones perception...not the suggestions of others.

c) Not believing implies ones consent to suggested nihil-ism (Latin nihilo; nothing), which makes one a nihil-ist.

d) The foundation of "nothing" is jewish aka creatio ex nihilo (creation out of nothing)... https://en.wikipedia.org/wiki/Creatio_ex_nihilo

"The Tree of Life, or Etz haChayim (עץ החיים) in Hebrew, is a mystical symbol used in the Kabbalah of esoteric Judaism to describe the path to HaShem and the manner in which he created the world ex nihilo (out of nothing)."