Holmes urges himself and his readers to look deep within their souls to create enduring monuments to God's greatness. Such monuments don't literally have to be stately mansions; they could be works of art such as poems, for example. What matters is that the individual build something strong and enduring, worthy of the God-given talents with which he or she has been endowed by the Almighty.
Holmes goes on to urge that we must move on from the "low-vaulted past." His use of an architectural metaphor here maintains the theme of building something new and grand in one's soul, not just as an act of praise to God but as a preparation for death. For even each "new temple, nobler than the last" must one day be left behind—just as the chambered nautilus withdraws into the outermost compartment of its shell—as we ascend to heaven, there to experience complete freedom and repose.