Baruch (aka Benedict di) Spinoza believed that there is only one substance in the universe, which he called God or Nature. Its substance has an infinite number of attributes. Rooted in this, he referred to the divine geometry method of reason, a rigorous, geometrical method of reasoning to derive his ethical conclusions. The outcome is essentially deterministic and rejected "free-will". 
He also introduced the concept of "conatus," which is the inherent drive of each thing to persevere in its being. For humans, this is expressed as the desire to maintain and enhance their existence.
He reasoned then, that an ethical life is one lived in accordance with reason. By understanding the true nature of reality (that everything is part of God/Nature, operating according to necessity, and is interconnected/ interbeing with all other things), individuals can achieve peace of mind and freedom/ true happiness. The highest form of knowledge is understanding things through their eternal and infinite aspect, which he equated with the intellectual love of God. 
He also viewed emotions and passions as natural phenomena that can be understood and managed through the same reasoning and believed that by understanding the causes of our emotions, we can gain control over them and achieve a state of peace.
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