Final answer:
The central idea of the passage is that the sonnet form was adapted to fit the English language, which led to the Shakespearean sonnet structure.
Step-by-step explanation:
The central idea of the passage in question is that the adaptations of the sonnet form were influenced by the necessity to adjust the structure to accommodate the English language, rather than Shakespeare's personal innovations. This adaptation process occurred when the sonnet was introduced to England by Sir Thomas Wyatt and Henry Howard, Earl of Surrey, and further developed by Shakespeare. This concept can be summarized by understanding that linguistic differences between Italian, the language in which the sonnet form was originally composed by Petrarch, and English necessitated technical modifications that eventually resulted in the Shakespearean sonnet.