西谷啟治在 1961 年所出版的《宗教是什麼》，被譽為戰後日本京都學派最高的代表作，主要面對的是虛無主義、近代自然科學的世界觀以及基督宗教的人格神等問題，企圖以佛教空的哲學
來超越虛無主義，從根源的主體性來解決有關人、自然、神三者的分裂與矛盾，達到對近代的超克。
內在於京都學派的發展脈絡，西谷哲學乃是繼承西田幾多郎絕對無的哲學與田邊元的種的論理，並進一步往前發展的，前者從自己與超越的次元的直接的、垂直的關係出發，開顯絕對無的場所；後者則是以社會、國家、罪意識、懺悔作為絕對的媒介，從這些學問、知識等世俗的、水平的次元，經過不斷的粹鍊，最後才契入到宗教的絕對無。
西谷的立場不外是交錯地運用這兩種開顯實在的垂直與水平之道，所展現出來的空的哲學。本文即是從西田哲學的純粹直觀、絕對無的場所之所以產生的脈絡出發，來探索西谷哲學產生的原點；接著闡述田邊元如何批評西田哲學，而進一步提出種的論理和懺悔道的哲學。最後分析西谷如何突顯空的場所和意識的場所、虛無的場所之間的差異，由此來看內在於京都學派的哲學，
西谷如何將「理事無礙法界」的哲學思惟，進一步推到「事事無礙法界」的境界。

Nishitani Keiji’s great work Religion and Nothingness, published in
1961, is to be praised as the most important representative work of the
Kyoto School after World War II. Facing the problems about the
nihilism of western philosophy, the world view of modern natural
science and the personal God of Christianity, Nishitani tries to resolve
the cleavage and contradiction among man, nature and God, rising in
the modern civilization, to overcome modernity from his philosophy
of fundamental subjectivity.
On the line of development of Kyoto School, Nishitani inherits
Nishida Kitaro’s philosophy of absolute nothingness and Watanabe
Hajime’s philosophy of logic of species and presents his philosophy of
Śūnyatā further. Nishida starts his thinking from the direct and vertical
relation between self and the transcendental dimension and directly discloses the place of absolute nothingness. Whereas Watanabe takes society, nation, original sin and confession, which belong to the area of the secular knowledge and don’t touch the transcendental.