Final answer:
The professor's remark about nineteenth-century Christianity being like a ruin overgrown by jungle represents the perceived erosion of Christian influence due to the rise of scientific thought and modern skepticism.
Step-by-step explanation:
In Sartor Resartus, the professor's declaration that Christianity in the nineteenth century is "lying in ruins, overgrown with jungle," metaphorically alludes to the perceived decline and obsolescence of Christian beliefs and institutions in the face of modern challenges. Such challenges include the rise of scientific thinking, the evolution of society and its morals, and the scrutiny of religious narratives by scholars and reformers of the time. This imagery of Christianity as a once-great structure now in ruins serves to emphasize the cultural and intellectual upheaval that was taking place during this era, wherein traditional beliefs were being questioned and often replaced by new ideologies and discoveries. Writers like Arthur Hugh Clough and William Wordsworth expressed this tension between old and new worldviews in their poems, reflective of the broader societal shifts.