Why is it canonical?

De Rerum Natura, or The Nature of Things, is an epicurean didactic poem that outlines Epicurean philosophy and metaphysics. It introduces the idea of particles, or atoms, forming the basis of all things. This concept of "atomism", as well as the discussion of the Epicurean tent of seeking pleasure, had an outsized influence on humanist thinkers seeking an alternative to the philosophy and teachings of scholasticism and church doctrine.