Giovanni Pico della Mirandola – Oration on the Dignity of Man
This short text is informally called the manifesto of the Italian renaissance. Pico della Mirandola was a brash twenty-something when he wrote this, and more than a little bit of a pedant. But all the hallmarks of renaissance thought are there—human-centered rather than god-centered; engaged with Greek and Roman classics, previously forbidden or forgotten in the Christian world; ditto Arabic and Jewish texts; a flowery, ornate prose style; a belief in progress and perhaps even the perfectibility of man; and a general spirit of can-do audacity.
All of these were breaks with medieval tradition, and an important step on the way to Enlightenment-style modernity.