The Antichrist was published by Nietzsche in 1888 and claims in its author's forward to be before its time, which it is. It was written during a time when to designate a book as "anti-Christ" or "anti-Christian" would have represented a great evil in Germany. Nietzsche suggests that in order to properly appreciate the work, one might have to be the kind of person who appreciated his prior work Zarathustra, and adds that for truly groundbreaking ideas, a true reception often has to be posthumous.
Historically, this work, along with Nietzsche's many other writings, represents what eventually became a great advancement in the fields of nihilism, and after that, existentialism. Nihilism is the philosophy that most closely defines Nietzsche's philosophical arguments en masse, stating that firstly, that man's belief in God is unfounded and wrong, and therefore, that our understanding of morality, of purpose, of meaning, are also wrong.
Instead of these primitive concepts of how one ought to regard the human experience, Nietzsche offers an alternative argument, perhaps rooted in the Darwinistic view which was articulated 30 years early in the Origin of Species, which states that the primary function for the progression of life is the survival of the fittest through competition. Although the book offers a robust exposition of the consequences of this argument, its core contribution to the literary and philosophical community is that it understands Christianity to be a worldview that privileges the weak. Christianity under this conception is fictional and contrary to the truth of nature, which is that the only moral value in life is power and control.