While Nietzsche injects myriad ideas into the book, a few recurring themes stand out. The overman (Übermensch), a self-mastered individual who has achieved his full power, is an almost omnipresent idea in Thus Spoke Zarathustra. Man as a race is merely a bridge between animals and the overman. Nietzsche also makes a point that the overman is not an end result for a person, but more the journey toward self-mastery.
The eternal recurrence, found elsewhere in Nietzsche's writing, is also mentioned. "Eternal recurrence" is the possibility that all events in one's life will happen again and again, infinitely. The embrace of all of life's horrors and pleasures alike shows a deference and acceptance of fate, or Amor Fati. The love and acceptance of one's path in life is a defining characteristic of the overman. Faced with the knowledge that he would repeat every action that he has taken, an overman would be elated as he has no regrets and loves life. Opting to change any decision or event in one's life would indicate the presence of resentment or fear; contradistinctly the overman is characterized by courage and a Dionysian spirit.
The will to power is the fundamental component of human nature. Everything we do is an expression of the will to power. The will to power is a psychological analysis of all human action and is accentuated by self-overcoming and self-enhancement. Contrasted with living for procreation, pleasure, or happiness, the will to power is the summary of all man's struggle against his surrounding environment as well as his reason for living in it.
The book in several passages expresses loathing for sentiments of human pity, compassion, indulgence and mercy towards a victim, which are regarded as the greatest sin and most insidious danger. Part of Nietzsche's reactionary thought is also that the creature he most sincerely loathes is the spirit of revolution, and his hatred for the anarchist and rebel.
Many criticisms of Christianity can be found in Thus Spoke Zarathustra, in particular Christian values of good and evil and its belief in an afterlife. The basis for his critique of Christianity lies in the perceived squandering of our earthly lives in pursuit of a perfect afterlife, of which there is no evidence. This empiricist view (denial of afterlife) is not fully examined in a rational argument in the text, but taken as a simple fact in Nietzsche's aphoristic writing style. Judeo-Christian values are more thoroughly examined in On the Genealogy of Morals as a product of what he calls "slave morality."