Both Uses of

Puritans
in
Invisible Man, by Ellison

Susie Gresham, Mother Gresham, guardian of the hot young women on the puritan benches who couldn't see your Jordan's water for their private steam; you, relic of slavery whom the campus loved but did not understand, aged, of slavery, yet bearer of something warm and vital and all-enduring, of which in that island of shame we were not ashamed-it was to you on the final row I directed my rush of sound, and it was you of whom I thought with shame and regret as I waited for the ceremony to begin.†
Chpt 5 *

Puritan = an English Protestant who in the 16th and 17th centuries wanted more purity and less ritual in worship, and who stressed hard work above pleasure

She was slipping out of her coat now, looking earnestly into my face, and I thought, Is she a Salvationist, a Puritan-with-reverse-English?†
Chpt 19

Definitions:

(1) (Puritans)
English Protestants who in the 16th and 17th centuries wanted more purity and less ritual in worship, and who stressed hard work above pleasure

(a Protestant is any of the Western Christian religious denominations that broke off from the Catholic Church. In the US, the best known are Baptists, Methodists, Presbyterians, and Episcopalians.)
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

As a common noun (not capitalized unless at the start of a sentence), puritan or puritanical can refer to someone who is very strict -- especially about religious principles or proper behavior.