Final answer:
Augustine and Monica's shared vision is the distinction between the Earthly City and the Heavenly City in 'The City of God.' This vision was significant as it provided Christians reassurance of an unshakeable Heavenly Kingdom during the fall of the Roman Empire, emphasizing the inferiority of earthly pursuits compared to eternal salvation.
Step-by-step explanation:
The vision shared by Augustine and his mother Monica is represented in Augustine's text 'The City of God.' It is the vision of the existence of two cities: the Earthly City and the Heavenly City. Monica represents the ideal Christian maternal figure, who guided Augustine toward the religious and philosophical thinking that led to his concept of the two cities. The Earthly City symbolizes the flawed and imperfect human society, characterized by pride and self-love. In contrast, the Heavenly City is seen as the domain of those who forego earthly pleasure and dedicate themselves to the eternal truths of Christian faith. This vision is significant because it reassured Christians, who were witnessing the fall of the Roman Empire, that earthly kingdoms might crumble, but the Heavenly Kingdom, the society of believers, would remain intact. For Augustine, all earthly matters, including the pursuit of knowledge, were subordinate to the ultimate goal of salvation and the eternal peace offered by the Heavenly City.