The book titled "Explanation of Fundamentals of Religion" by Imam Abi Taher Ismael bin Moussa Al Gitali on explaining the poem of Abi Nasr Al Maloshaey was written in explanation of the poem of Abi Nasr which addresses theology in (180 lines). He explained it in three parts. He addressed in detail the linguistic rhetoric of the lines and cited the numerous quotes of scientists as well as substantiation by the mental arguments after Quran and Sunna. The study is in two parts: Study and investigation. The study is divided into two sections, the first address the characteristics of Allah, Almighty. It defined characteristics in language and terminology, and mentioned the divisions of characteristics and personal characteristics and difference on them as well as the similar characteristics and opinions of scientists on them. Chapter two addressed the matter of custody and innocence. Custody was defined and its sections were mentioned, then innocence and its sections. The study also dealt with full stop and its types, including the opinion of Imam Al Gitaly on the two topics. Section two was an investigation of the body of the book from the section of (significance of names) up to the (the question of: If two trustees gave witness on a group). The key results of the study stated that copies of the book of fundamentals of theology are fourteen, including the complete, the deficient and some of them are copies of the imams of knowledge. Concerning his approach in explanation of the book of theology, it combined the long explanation and quotation. It redundantly explained the poem lines in language and cited versions of the Holy Koran and Prophet Hadiths as well as consent and poetry lines. Quotation from the key books of the people of knowledge scientifically ordered their chapters and sections, and sometimes discusses the matters and reviews the argument of the opponent and reply to them by mental argument to reach persuasion. There is conformity in the methodology between the book of explanation of theology and the book of the Rules of Islam by Al Gitali on the matter of custody and innocence in terms of sections and content. However, it deliberately explained the book of explanation of theology