Final answer:
The question is focused on symbolism surrounding the Second Coming of Christ and Christian eschatology. While line 20 isn't specified, various textual and art references indicate the use of Christian symbols to convey divine events.
Step-by-step explanation:
The question appears to be related to literary analysis, specifically concerning symbolism in a text that may reference 'The Second Coming' or symbols associated with eschatology. Without the specific text of line 20, it's not possible to provide the exact symbol in question. However, the excerpts provided indicate a strong focus on Christian eschatology, particularly the Second Coming of Christ, as well as other symbols associated with the Christian faith such as the cross, angels, and other iconography described in various religious texts and artworks that symbolize mourning, holy intervention, and divine presence.
These symbols often represent deep spiritual meanings and are used to convey the immense power of divine events. References to Christ in a medallion and the Transfiguration signify the divine nature and holy authority of Jesus in Christian theology. Dr. Zucker and Dr. Harris' mention of Christ looking past us and figures emerging from tombs in a tympanum evoke the imagery and symbolism of the Last Judgment, signaling the finality of divine judgment.
Finally, the description of millennial sects, like the Mormons and Shakers, holding eschatological beliefs and the mention of William Miller setting a date for the Second Coming highlights the profound impact such symbols and associated beliefs have had on religious groups and societies throughout history.