The oneness of God, its requirements and nullifiers

This book The science of monotheism: the noblest of sciences, and the most honorable in rank, and the most obligatory in pursuit; because it is the knowledge of Allah the Exalted, His names and attributes, and His rights upon His servants, and because it is the key to the way to Allah the Exalted, and the foundation of His legislation upon which it is built. And it is the most important reason for steadfastness in life and after death. As for in life: it is the stronghold from falling into deviation and misguidance. And after death: it is the most important reason for salvation from the punishment of the grave and its trials, and what follows it. And since this is the nature of monotheism, it is obligatory upon every Muslim to learn it, and to act according to it, first in general, so that he builds his religion on a sound basis, and with reassurance and submission, happy with its fruits and results in this world and the Hereafter. Ibn Kathir - may Allah have mercy on him - said: (Those who sincerely worship Allah alone and do not associate anything with Him, are the ones who will be safe on the Day of Resurrection, guided in this world and the Hereafter). And I have seen - seeking help from Allah the Exalted and inspired by His pleasure and success - an approximation of this knowledge, and arranging its issues in a concise and easy manner, relying on the texts of the two revelations, clarifying this with some words of the scholars, and I named it (Monotheism: Its Necessities and Its Nullifiers).