In no way, I think, does Spinoza give the best proof that God exists. Probably very few believers would say that. Spinoza just gives the argument that makes the most sense/like the most to people who usually don't believe in God.

This is also similar to... Advaita Vedanta... Everything is One.

The word Advaita is a composite of two...

Hilarious!

Now if you believe that God is an old guy with a white beard in the Sky who created everything and waits to judge you at the end your life then this view of Spinoza’s may be a very difficult concept to grasp.

That's not a common belief, as far as I know. It's one thing for them to represent God that way...

Interesting topic you have brought up. Cheers!