Today’s reading is drawn from Ezekiel 9:3-4 and Revelation 18:16-18.
Whereas the mark on the righteous was to protect them in Ezekiel 9:4–6 and some other texts, also includes a mark of destruction on the forehead of the wicked. These marks were symbolic signs visible only to God and his angels, not to people. The use of a mark to enforce national or empire-wide unity already had a long history that would be known to John’s audience.
Ancients, including some Diaspora Jews such as Philo, were adept at using symbolic numbers and calculating special numbers. Scholars offer various connections. The number 666 is a doubly triangular number (there are only four such numbers between 100 and 1,000). Geometers valued triangular numbers just as they valued square numbers. Just as any number with the same number of identical units vertically and horizontally forms a square, a triangular number is one in which the top level has one unit, the next level has two, the next has three, and so forth, so that one can form with it something like an equilateral triangle. The triangular number with a base of 36 units is 666; the triangular number with a base of eight is 36, so that 666 is not only triangular but has a triangular number as its base.
The number 666 is also almost two-thirds of 1,000, and Revelation sometimes calculates judgments in thirds (Revelation 8:7–12; 9:15,18). Thinkers as early as the second century suggested that six here might function as an evil parody of seven (a key number in Revelation). Indeed, calculated as a number, the name “Jesus” comes to 888.
Others argue that the invitation to calculate the number (Revelation 13:18) points to a particular name. Both Greek and Hebrew used letters also as numerals, so one could add up the letters in a name as numbers, as many Jewish thinkers did. One Jewish prophecy tradition treated names of various rulers as numbers. People in the empire played on the number of “Nero Caesar” in Greek letters. There are two ways to spell “Nero Caesar” in Hebrew letters; one comes out to 666, and the other to 616.