One of the primary differences between Renaissance and Medieval (Pre-Renaissance) literature is the rediscovery of texts from classical antiquity. In the Middle Ages, there was extreme attention given to Biblical and religious texts, while writers largely dismissed the great writers of the past because they were pagan.
This began to shift during the Humanist period in Italy, when Dante, Petrarch and Boccaccio began to examine classical writers within the context of religious themes; thus we have the Roman poet Virgil as Dante's guide through Christian Hell in his Inferno.
The discovery of Plato (who was largely lost during the Middle Ages) in the Renaissance led to Neo-Platonism in the Renaissance, which proved to be very compatible with Christian ideology due to the idea that the more perfect soul is trapped inside the corrupt body. Not only did this influence literature, but also the other arts, as seen in both Michelangelo's poetry and sculpture.
Literature in the Renaissance also began to be more personal and examined, as Petrarch wrote sonnets about his own individual condition in his Rime sparse, evoking the first person singular in reference to his melancholy disposition. This proved to be an early indicator of what would come in modern literature.