Judaism, like any philosophy, is an evolving field of concepts stimulated by debate. Likewise, it also harbors its fair share of staunch opponents to change. For a significant portion of its existence, Judaism has struggled to define itself. As the world around the earliest Judaic documents changed and new ideas filtered into the intellectual communities that studied Torah, Jews began to struggle with the very definition of what is and what is not Judaism. Our greatest philosophical documents, like the tractates of the Talmud, are nothing if not debates between great thinkers. However, some great thinkers were never even invited to the table because their ideas were too radical for their contemporaries. Among the most influential, controversial figures in not only Jewish thought but philosophy as a whole, few are as well-known as Baruch "Benedictus" Spinoza.
Many of the Person of the Week features talk about the contributions and struggles of Spanish and Portuguese Jews in and around the Renaissance. Indeed, Baruch Spinoza's family came from that same Sephardic tradition and were almost certainly Conversos. Baruch's grandfather, Isaac, moved his family from Lisbon to Amsterdam where they could practice Judaism without as much scrutiny as in Portugal, Spain, Italy or France. His father, Miguel, was a merchant who eventually died at war. Baruch was born in 1632 and at the age of 24 was already widely known for his unusual beliefs. The Jewish community of Amsterdam issued him a cherem, an excommunication, for the heresy of his published works.
The cherem differs from the kind of excommunication practiced by the Catholic Church, if only in its intent. Unlike the dominant faiths of the time, Judaism had no political refuge in the world. The Catholic Church especially focused on Jews who courted controversy to demonize Judaism as a whole. Spinoza's ideas were radical enough that they drew the ire of religious non-Jews, thus all the dangers that come with that attention.
So, what were these controversial ideas? Put in simple and unfortunately inadequate terms, Spinoza was heavily influenced by Rationalist philosophy and contended that, among other things, God and Nature are one in the same. This runs contrary to a central Jewish tenet that God is unique to everything else. In more elaborate terms, Spinoza's concept of God/Nature unity shifted the focus of divine authority. The traditional model, which is still largely held today, is that God is an active authority issuing law. Spinoza's concept is that God's laws are actually the laws of nature.
While this element of Spinoza's philosophy remains controversial, some of his other ideas have recently come to be much more widely accepted. For instance, he opposed the Cartesian model that states mind and body are two completely separate entities. Spinoza wrote that, all things in the universe being of a single substance (God/Nature), the mind and body are actually a single entity. With modern science, we today have come to understand many of the physical properties of that which we call the mind, including neurochemistry, the role of electricity in brain function, and the discreet centers of individual functions in the brain.
The big question surrounding Baruch Spinoza is whether or not we can really call him a Jew. Is his philosophy so divergent from Judaism that he no longer qualifies? Personally, I'm not so ready to excommunicate Spinoza as the Jews of Amsterdam were. Call his philosophy what you will, Spinoza's chief aim was to discover the truth and achieve a measure of harmony with the world around him. He held knowledge, even wisdom, to be the highest attainable virtue. For those who would lump Spinoza in with the atheists of later philosophies, take into account his understanding of truth and the human capacity to understand it. In the most pithy possible definition, Spinoza believed that to acquire new knowledge is to be blessed. If you believe in God and come to find something to be true, is it possible for that truth to issue from anywhere but God?