Using the term "Necessary Existent" for God is one of the most important innovations that Avicenna brought into philosophical and theological thought. The term Necessary Existent has been widely accepted in both Islamic and Western tradition and has been at the center of discussions such as the ontological argument, cosmological argument, divine simplicity, the distinction of quiddity and existence, and the debate whether ‘exist’ is a predicate or not. One of the main issues discussed in the tradition of commentaries and glosses on the short and concise work of Nasir al-Din al-Tusi named Tajrid al-I'tiqad, which has become one of the most powerful and long-lasting mediums in which metaphysical debates are carried out in late-period Islamic thought, is how to understand the necessity of the Necessary Existent. The core of the debate is based on the problem of whether there is a contradiction between the simplicity and necessity of God. On the one hand, saying that God's existence and quiddity are identical, and on the other hand, defining God's necessity as requiring the existence by his quiddity/self may lead to the conclusion that there is a contradiction between simplicity and necessity at first sight. The purpose of this article is to analyze the views of three important commentators of al-Tusi, al-Isfahani, al-Qushji and al-Dawani, about the necessity of the Necessary Existent in terms of divine simplicity. In addition, a brief, critical evaluation of the method to be followed in classical Islamic thought studies is also made in the introduction.