John was a pharmacy technician
John realized in time that more needed to be done to educate people in the faith. He formed an organization (which he called a confraternity) to develop and compile teaching materials and methods to instruct people in Christian doctrine.
Never afraid to minister to the sickest of the sick, even in his sixties, John Leonardi died of plague on this very day exactly four hundred years ago. The very name Confraternity of Christian Doctrine (CCD) would become synonymous with teaching within the Church, even to the present time. Saint John Leonardi was canonized in 1938.
(adapted from an earlier post)