I [heart] metaphysics!

Here, have an ontological argument from Spinoza's Ethics:

Proposition 11. God, or substance consisting of infinite attributes, each one of which expresses eternal and infinite essence, necessarily exists.

Demonstration. If this be denied, conceive, if it be possible, that God does not exist. Then it follows that His essence does not involve existence. But this is absurd. Therefore God necessarily exists. Q.E.D.

For newbies, an ontological argument is taken to be a statement purporting to "prove" the existence of God. (Think of a geometrical "proof" and you've got the idea.) And on some level, that's exactly what it is. But the other purpose for the ontological argument is that it serves as the foundation for a specific theology. It's the statement of a worldview, usually with God at the center.

The basis of Spinoza's theology is not God's existence; it's that God is existence. The proof of God's existence is that existence, well, exists. At the same time, it's a statement about the divine nature of existence.

***

One of the basic premises of pantheism, especially as constructed by the Stoics, is that one of God's attributes (even the main one, depending on who you ask) is Reason. Justin Martyr, a Stoic of the Christian tradition, decided that since Christ was the embodiment of Logos, anyone who ruled their life through the use of Reason was a good Christian. This even included pre-Christian philosophers like Heraclitus and Socrates. (A popular theory among Jewish and Christian philosophers of the time was that the early Greeks had somehow gotten their hands on the Torah, and that's why Greek philosophy made so much sense!)

Spinoza developed this further by explaining (in his usual convoluted way) that Reason and reality are just two sides of the same coin.

From part 2 of the Ethics:

Proposition 7. the order and connection of ideas is the same as the order and connection of things.

... [E]verything which can be perceived by the infinite intellect as constituting the essence of substance pertains entirely to the one sole substance only, and consequently that substance thinking and substance extended are one and the same substance, which is now comprehended under this attribute and now under that. Thus, also, a mode of extension and the idea of that mode are one and the same thing expressed in two different ways ... .

[Gesundheit.]

Spinoza, of course, lived shortly after Descartes, who (in)famously decided that mind and body were completely separate--thus creating a paradox that philosophy wasted hundreds of years trying to solve (a guy named Malebranche, for instance, turned God into a phone switch operator between mind and body). Spinoza's two-sided coin doesn't say that mind and matter coincide, or are connected, or are best buddies. They're the same sentence, spoken in two different languages.

Unlike in classical theism, Logos doesn't come in to redeem the world; Logos is the world.

Marcus Aurelius says, "Never let the future disturb you. You will meet it, if you have to, with the same weapons of reason which today arm you against the present."

***

In the Appendix to the first part of his Ethics, Spinoza has this to say:

...[I]t is commonly supposed that all things in nature, like men, work to some end; and indeed it is thought to be certain that God Himself directs all things to some sure end, for it is said that God has made all things for man, and man that he may worship God. ... This is the reason why each man has devised for himself, out of his own brain, a different mode of worshiping God, so that God might love him above others, and direct all nature to the service of his blind cupidity and insatiable avarice.

Thus has this prejudice been turned into a superstition and has driven deep roots into the mind--a prejudice which was the reason why everyone has so eagerly tried to discover and explain the final causes of things. The attempt, however, to show that nature does nothing in vain (that is to say, nothing which is not profitable to man), seems to end in showing that nature, the gods, and man are alike mad.

[Pause for three cheers!]

To broaden/deepen/support that, a verse from the Tao te Ching:

Nature is not kind;
It treats all things impartially.
The Sage is not kind,
And treats all people impartially.
Nature is like a bellows,
Empty, yet never ceasing its supply.
The more it moves, the more it yields;
So the sage draws upon experience
And cannot be exhausted.

The most important part of pantheist theology: God is not a Person.

As a last, rather funny note, here's what Spinoza thought about the devil, from his Short Treatise on God:

If the devil is a thing which is entirely opposed to God and has nothing from Him, he is absolutely indistinguishable from the Nothing of which we have already spoken. But, if we suppose with some that the devil is a thinking thing, who neither wills nor does anything whatever that is good, he is certainly most miserable, and if prayers could help him we ought to pray for his conversion.