6 ideas
People believe their choices are free because they are conscious of their desires and actions but ignorant of the causes that determine them. The feeling of free will is therefore a gap in knowledge rather than evidence of an uncaused choice, much as a thrown stone would think it flies by its own will if it were conscious.
Only one substance can exist, because a substance is defined as something that exists in itself and is conceived through itself, and two substances could not share an attribute or cause one another. Everything else, including minds and bodies, is a mode or modification of this single infinite substance, so God is not a creator standing outside the world but is identical with Nature itself.
Each thing, as far as it can by its own power, strives to persevere in its being, and this striving is the thing's actual essence. In humans the striving is called desire. Good and bad name whatever increases or decreases this power to act rather than naming anything valuable in itself.
All emotions derive from three primary affects. Joy is a transition to greater power of acting, sadness is a transition to lesser power, and desire is striving itself. Love is joy accompanied by the idea of an external cause and hatred is sadness accompanied by such an idea, so any emotion can be analyzed by asking what it does to your power and what you attribute it to.
A passive affect is a confused idea, and it ceases to be a passion as soon as we form a clear and distinct idea of it. Seeing that an event followed necessarily from a chain of causes weakens the anger, regret, or fear it provokes, because the emotion no longer fixes on one imagined free cause. Freedom is gained by understanding causes, not by exercising will against desire.
The mind's highest good is knowledge of God, meaning intuitive understanding of things as following from the whole of Nature, and this produces an intellectual love of God that is lasting joy. Blessedness is not a reward for restraining the passions. We are able to restrain them because we already enjoy this understanding.