The Testament of Reason is the second of the two Testaments of Faith; together with the Testament of Birthright, it is a lighthouse that guides us through the darkness of our inner worlds.  It is the “ultimate” Testament, the one that all the previous Testaments lead up to. The Fourth Testament assures us that, no matter how irrational or even destructive an action or thought of feeling seems, if we look hard enough, we can find Reason.  
But what is Reason? From Roman Catholic doctrine (as presented by a former SNL cast member) to the Enlightenment, we come to understand the facets of Reason; the ability to think, the ability to find a cause for things we don’t understand, and that causes and Reasons are found not only in the past, but also in the present. 
Human beings are always seeking to make meaning of their experiences, and finding meaning is the core of the Testament of Reason. Like the man who realized his social anxiety was really his inner warrior preparing him for battle, or the girl who was seeking her ancestors in a cloud of cigarette smoke, when we understand the hidden meaning of our behavior, we have the power to change.