Buddhism is monism but not monotheism. The former denies any fundamental duality while the latter is the doctrine that there is only one God. The two are quite different. Monism by far is the most subtle of the two. It can be illustrated by the ocean with its ever-changing waves. In other words, the simple element of water can become waves which are never the same—yet which are fundamentally only water. Waves, I would add, are accidents, that is, they are not essential to the nature of water. Only the water is real. All else is empty and illusory.
The entire cosmos is only Mind. What we see through this body we inhabit is empty and illusory—not essential to Mind. But all this is for a reason which shall be explained later.
All that we know and can see is what is empty and illusory. Just name and form (nāma-rūpa), a differentiation of the original Mind. In this predicament we are unable see our self. We only see guess-works of our self which amount to simulacra or representations of our self—never our true self which is Mind.
Despite this appalling condition there is a way out. This is what the Buddha discovered.
Since we are, intrinsically, Mind we have only to penetrate through this empty and illusory phenomenalization of Mind, namely, our agitated, ever changing thoughts, like a laser adjusting down on a dimensionless point. This is then like a door which opens to our self or Mind from whence we first began.
The seeing of this dimensionless point is suddenly followed by a flood of psychical, vital light that continues for many hours. What this all adds up to is that we have penetrated through the veil of mind phenomena. Using our previous analogy, instead of seeing waves, we enter the water which we always were; which is where we began. Now when we look at this ocean, even with its waves, we only see water.
The One Mind in order to behold itself first causes a contrast by phenomenalizing itself—creating as it were a false other. Then confronted by its own phenomena it passes through it and out of it returning to itself. By this return phenomena is saved, so to speak. It was always heuristic. But the big payoff is freedom from further suffering. Nothing changes yet everything changes.