Which theoritecal thoughts help me the most to understand the fourteenth century literature in relation to politics in Chaucer's poetry?
The 14th c. in England was pre-Reformation, and the prevailing powers--the Catholic church and the English monarchy--were beginning their disagreements, which would come to a climax with Henry VIII’s desire for a divorce, and Rome’s refusal, in the 16th c. Added to this growing tension was the gradual strengthening of the power of Commerce, as fueled by trade with the East. Chaucer took this social unrest and added the complication of individual personalities (together with their follies, pettiness, and hypocrisies) on a journey that was, for most of the characters, a hypocrisy all by itself. Given the corruption in the Church (selling indulgences, for example), and the common people’s powerlessness against the injustices of the monarchy (excessive taxation, for example), the political climate was ripe for a popularist satire of this sort. As for “theoretical thoughts,” besides the Church doctrines, you might look at Boethius’ 6th c. “The Consolation of Philosophy” and Robert Mannyng’s “Handlyng Synne” (1303), two highly influential documents of the period.