Since 1677, the year of the publication of Ethics, Spinoza's ideas have sparked, following the most varied directions, an unceasing interest to this day. However, these ideas have often been approached detached from the evidential framework that supports their exposition, due to the intensely technical nature and dry style of this framework. This book, which aims to serve as a working tool for those seeking more direct access to Spinoza's text, provides all the explanations that are absolutely necessary for reading the first part of Ethics, in which, under the title "Concerning God," an attempt is made to study reality as a whole, starting from the rational and causal principle that simultaneously grants it its internal unity and its absolutely necessary character. This part of Spinoza's book, which is particularly difficult and enigmatic due to its relative brevity, plays an essential role in the overall economy of Ethics: it is what provides the program of ethical liberation with its objective basis, deeply grounding it in the nature of things.