Pantheism and Monism
   
Pantheism is the belief that all existing things are in some sense divine.  In other words, all beings are divine or God is in everything. A classical expression of such pantheism is the philosophy of the Stoics of ancient Greece.  They taught that there is one sacred being which they called the Logos.  Put simply, they believed that a little bit of the Logos  - a “spark of the divine” was in everything.  All objects are separate from the Logos, even though they may participate in the divine. 

On the other hand, monism in the strictest sense is the belief that only One Being exists. Whereas pantheism is the belief that God is in all the separate and distinct objects that make up the cosmos, monism believes that the only thing that exists is God; in other words, there are no separate objects.

Pantheism and Monism in the Hindu tradition
   
As we have noted earlier, Hinduism is an incredibly diverse collection of traditions and beliefs.  It should come as no surprise, therefore, that both pantheistic and monistic conceptualizations of the sacred are found in Hinduism.

The latest writings of the Hindu scriptures are known as the Upanishads (probably written down around 500 BCE). These are largely philosophical discourses and dialogs that reflect on many important concepts including the nature of humanity and the nature of the divine. The basic underlying theme of the Upanishads is that the human soul (atman) is part of the universal sacred power (Brahman).  Although stopping short of claiming absolute unity, the Upanishads argue the the atman emanates from the Brahman, and thus the two share the same nature. Consequently, one may look within to discover the great soul of the universe .

The Pantheism of the Upanishads indicates that the seeming polytheism of Hinduism is distinct from the type of polytheism where each god or goddess has its own realm of power.  Rather, in Hinduism, each deity is a manifestation of the sacred power (Brahman).  As such, they are not completely separate from one another.  Moreover, because the universal sacred power is present, each deity also represents the fullness of Brahman.

In the Eighth Century AD, the philosopher Sankara (788-820), formulated a philosophic system known as Advaita Vedanta.  According to this philosophy there is an absolute unity between Brahman and atman.  In fact, the only reality that exists is Brahman.  Our perception that we are separate beings from Brahman and from one another is in fact an illusion. To a large extent, this philosophic system is non-theistic; that is, it does not emphasize the notion of a deity or deities that have a separate existence.

Please note that the above discussion is not meant to imply that Hinduism progressed from pantheism to monism. Like many concepts in Hinduism, pantheism and monism exist side by side.