Essential

  • ●indispensable
  • ●requisite
  • ●imperative
  • ●main
  • ●significant
  • ●main ingredient
  • ●vital
  • ●obligatory
  • ●all-important
  • ●intergral
  • ●fundamental
  • ●key to ___
  • ●the ___ bible
  • ●critical
  • ●a prerequisite of