The reality of faith has long been a subject of debate among theologians, with various opinions proposed regarding its relationship with action and the role action plays within faith. This study re-examines the reality and definition of faith through the lens of the philosophy of action (also known as action theory), which investigates the nature of human action, agency, will, and the connection between mental states and physical movements. Given that religious action is the outcome of religious faith, we philosophically analyzed the principles of action and human will in Mulla Sadra's works. This philosophical re-reading reveals a profound connection among knowledge, action, and faith. We demonstrate that knowledge (ma'rifat) serves as the foundational prerequisite for realizing faith, while action acts as its necessary consequence. Most importantly, we identify intensified desire (shawq mu'akkad) as the very essence of faith. Finally, we compare this re-examined definition with Mulla Sadra's original formulations in his texts. The findings show that analyzing faith through his philosophy of action not only clarifies the deeper dimensions of faith but also aligns seamlessly with his broader metaphysical framework.