The name “Formalist” is a term sometimes used by the Puritans to denounce a merely outward religion, as opposed to religion of the heart. The Celestial City is sometimes referred to as Mount Zion, a biblical metaphor for Heaven. With this in mind, it’s clear that both Formalist and Hypocrisy (i.e., one whose practice of religion doesn’t match what he professes to believe) think it’s possible to reach Heaven by pretense. As long as they
appear to have lived religiously, in other words, that should be enough to get them into Heaven. Christian warns them that their pretense will be found out.