Writing in theTreatise on the Emendation of the Intellect, Spinoza says that our well-being and happiness, indeed our ultimate perfection, consists in a certain state of knowing. Above all, we need to understand ourselves and the nature and powers of the human mind. But, he insists, this will come about only when we understand the natural order of which we are indelibly a part, and especially the highest causes from which all things bodily and spiritual follow.

The highest good for a human being is the knowledge of God and Nature.

Establishing this conclusion with demonstrative certainty is the main project of the Ethics. And in Part One, Spinoza takes the first step of his project by proving the most general and important metaphysical truths about God and Nature. His startling conclusion is that, in fact, God and Nature are one and the same thing. Rather than speaking of ‘God and Nature,’ as if they are distinct, we should in fact speak of ‘God or Nature,’ Deus sive Natura, where the two words are simply different ways of referring to one subject.