structural:expansion, information:filtering, structural:scholar_edition, linguistic:voice_change
Correspondence

Few of Spinoza's letters are extant, and none before 1661. Nearly all the contents are philosophical and technical because the original editors of Opera Posthuma —a collection of his works published posthumously—Lodewijk Meyer, Georg Hermann Schuller, and Johannes Bouwmeester, excluded personal matters and letters due to the political and ecclesiastical persecution of the time. Spinoza corresponded with Peter Serrarius, a radical Protestant and millenarian merchant, who was a patron of Spinoza after his expulsion from the Jewish community. He acted as an intermediary for Spinoza's correspondence, sending and receiving letters of the philosopher to and from third parties. They maintained their relationship until Serrarius died in 1669.

Through his pursuits in lens grinding, mathematics, optics, and philosophy, Spinoza forged connections with prominent figures such as scientist Christiaan Huygens, mathematician Johannes Hudde, and Secretary of the British Royal Society Henry Oldenburg. Huygens and others notably praised the quality of Spinoza's lenses. Spinoza engaged in correspondence with Willem van Blijenbergh, an amateur Calvinist theologian, who sought Spinoza's view on the nature of evil and sin. Whereas Blijenbergh deferred to the authority of scripture for theology and philosophy, Spinoza told him not solely to look at scripture for truth or anthropomorphize God. Also, Spinoza told him their views were incommensurable. Gottfried Wilhelm Leibniz outwardly described Spinoza's work negatively but privately wrote letters to him and desired to examine the manuscript of the Ethics. In 1676, Leibniz traveled to The Hague to meet Spinoza, remaining with him for three days to converse about current events and philosophy. Leibniz's work bears some striking resemblances to parts of Spinoza's philosophy, like in Monadology. Leibniz was concerned when his name was not redacted in a letter printed in the Opera Posthuma. In 1675, Albert Burgh, a friend and possibly former pupil of Spinoza, wrote to him repudiating his teachings and announcing his conversion to the Catholic Church. Burgh attacked Spinoza's views as expressed in the Theological-Political Treatise and tried to persuade Spinoza to embrace Catholicism. In response, Spinoza, at the request of Burgh's family, who hoped to restore his reason, wrote an angry letter mocking the Catholic Church and condemning all religious superstition.

Spinoza published little in his lifetime, and most formal writings were in Latin, reaching few readers. Apart from Descartes' Principles of Philosophy and the Theologico-Political Treatise, his works appeared in print after his death. Because the reaction to his anonymously published work, Theologico-Political Treatise, was unfavorable, Spinoza told supporters not to translate his works and abstained from publishing further. Following his death, his supporters published his works posthumously in Latin and Dutch. His posthumous works– Opera Posthuma –were edited by his friends in secrecy to prevent the confiscation and destruction of manuscripts. He wore a signet ring to mark his letters, engraved with the Latin word Caute, meaning "Caution", and the image of a thorny rose.