Nomani's Kitab al-Ghaybah is a foundational text on the doctrine of occultation, particularly the Major Occultation of Imam Mahdi (a.s.), the awaited savior in Shia Islam. Through narrations and scholarly perspectives, Nomani delves into the theological reasons behind the Imam’s concealment and the signs of his eventual return. The book emphasizes patience and faith, providing clarity on the responsibilities of believers during the occultation period while awaiting divine justice and ultimate salvation.