BibTeX:
@incollection{ShoghiEffendi1939,
  author = {Shoghi Effendi},
  title = {The Most Vital and Challenging Issue},
  booktitle = {The Advent of Divine Justice},
  year = {1939},
  publisher = {Bahá'í Publishing Trust},
}

APA:
Shoghi Effendi. (1939). The Most Vital and Challenging Issue. In *The Advent of Divine Justice*. Bahá'í Publishing Trust.

MLA:
Shoghi Effendi. "The Most Vital and Challenging Issue." *The Advent of Divine Justice*, Bahá'í Publishing Trust, 1939.

Chicago:
Shoghi Effendi. "The Most Vital and Challenging Issue." In *The Advent of Divine Justice*, Bahá'í Publishing Trust, 1939.