Spinoza's philosophy aims to reform understanding, religion and politics. If you had to buy it with Descartes, you differ from this one by taking care of politics, excluding scientific issues.
Spinoza is inspired by manuals of Euclidean geometry, which reveals his method: everything must be reduced geometrically from the idea of God, which is an innate idea. On the other hand, in clear pantheism, everything comes from God and everything remains in him. Reason is conceived as merely deductive and mathematical, aspect in which it is possible to find the greatest similarities with respect to Descartes.
Spinoza is perhaps, a mystic amazed by reason... or rather, a rationalist inspired by mystical intuitions.
Deus, lives Substance, sive Natura, the famous formula of Spinoza expresses a notion of God different from that of Scholastica and even that of Descartes. God is Nature, Nature is one Whole, one Substance. Things are but “immanent” parts of the Whole.
The universe of Spinoza is therefore pantheism since it resurfaces in the idea of reality as infinite Totality.
While for scholastics, the substance was conceived as an “inert substrate”, Spinoza sees it as causality and strength. For his part Descartes had conceived finite substances as condemned to perpetual rest, and had explained their activity by deducing that the world of extension needed God to move it while thought needed the concurrence of will. What Spinoza will do is give dynamism to the Cartesian scheme in such a way that it identifies extension with movement and thought with thought.
In this way, the Substance (or Nature) is active and creative. The attribute (or what expresses the essence of the substance) of thought generates chained ideas that synthesize a single idea of God. And the extension attribute, produces an infinite series of movements: The order and connection of ideas is the same as the order and connection of things
For Spinoza, all attributes identify each other, in such a way that the problems arising from Cartesian dualism are avoided, since there is no point in wondering how things act on the mind or vice versa. In fact, if there is only one substance, its attributes, even if they are infinite, result in a single attribute (since they come from the same substance). Thus, each thing has an idea and that idea is its “soul”, so all beings would be animated to a different degree. The order of ideas, then, reflects the order of things and is also a necessary order: as necessity directs everything that happens in Nature, it is that it can be exposed in a geometric order. However, it should be noted that this “need” does not imply a “purpose”. Spinoza considers the cause efficient, rather than the final cause, since thinking that things happen for something... is nothing more than a game of imagination.
Spinoza will say that the human being must, first of all, be free from imagination, but what is imagination for Spinoza?
Imagination is any form of knowledge that, depending on the body itself (as it suffers the action of other external bodies) in such a way that only allows to know nature in a partial (fragmented) way.
All kinds of illusions come from imagination:
a. Teleologicalerrors: believing that the world is at the service of man
b. Axiologicalerrors: believing that notions such as “beauty” and “ugliness”, “evil” and “good” allow to know Nature.
c. Antlrologicalerrors: believing that man himself is a substance. If man were “auctionance”, the world would be made for him and consequently things would be good or bad according to whether they suit him or not.
Passion also arises from imagination and enslaves man. Love, sadness, joy or hatred dominate him and make him a slave to his passions, subjecting him to the course of the Universe.
But through thought, man can know the world, this means producing his own ideas. In this way, the mind abandons passivity, whereby the activity of the soul will not be without part of the activity of the infinite attribute of Thought. The human soul joins Nature, captures the Totality and sees it expand to prevent its own strength and power.
The knowledge of the Totality (or what is the same, the way in which each case is integrated into the Totality) is the right knowledge. That is why Spinoza will say that the true idea is the rightidea, differs at this point with Descartas who will talk about the clear and distinct idea.
When the human soul joins Nature, a boundless joy arises since man in the depths of his being is effort and desire... power and strength, and the effort is, before anything else, an effort to know God, thereby increasing the power of man and the joy is born from this increase of one's self.