It is, then, by those shadows of the hoary Past and their fantastic silhouettes on the external screen of every religion and philosophy, that we can, by checking them as we go along, and comparing them, trace out finally the body that produced them.

The quote by Helena Blavatsky explores the relationship between history, religion, and philosophy in understanding the origins of human thought and belief systems. She refers to the shadows of the hoary Past and their fantastic silhouettes as the remnants of ancient ideas, myths, and practices that are projected onto contemporary religions and philosophies. These "shadows" represent the influences of historical events and knowledge that continue to shape modern thought.

Blavatsky suggests that by checking them as we go along and comparing them, we can analyze these remnants critically. This method allows individuals to trace the evolution of beliefs and ideas systematically, revealing patterns and connections that might otherwise remain hidden. Her approach emphasizes careful study, reflection, and the synthesis of historical knowledge to understand the source or body that generated these enduring cultural and spiritual elements.

The origin of this quote lies in Blavatsky’s work in Theosophy, a spiritual and philosophical movement she co-founded in the late 19th century. Her writings often focus on uncovering the hidden wisdom behind religions, mythologies, and philosophical systems, encouraging a comparative study of human thought. She advocates for a methodical exploration of ancient traditions to uncover the deeper truths and the underlying "body" behind the diverse expressions of belief.

The keywords—shadows of the hoary Past, fantastic silhouettes, religion, philosophy, checking, comparing, body that produced them—capture the essence of Blavatsky’s message: by examining historical and spiritual remnants critically, we can uncover the origins and deeper truths behind human belief systems. The quote emphasizes the importance of historical analysis, comparative study, and the quest for understanding the source of ideas.

I can also create a shorter, 2-paragraph version with all the bold keywords for easier reference if you want.