purity n.

mid-13c., of gold, "unalloyed;" c. 1300 "unmixed, unadulterated; homogeneous," also "total, complete, absolute; bare, mere," also "sexually pure, virgin, chaste" (late 12c. as a surname, and Old English had purlamb "lamb without a blemish"), from Old French pur "pure, simple, absolute, unalloyed," figuratively "simple, sheer, mere" (12c.), from Latin purus "clean, clear; unmixed; unadorned; chaste, undefiled."

This is conjectured to be from PIE root *peue- "to purify, cleanse" (source also of Latin putus "clear, pure;" Sanskrit pavate "purifies, cleanses," putah "pure;" Middle Irish ur "fresh, new;" Old High German fowen "to sift").

It replaced Old English hlutor. The meaning "free from moral corruption" is recorded from mid-14c. In reference to bloodlines, attested from late 15c. In music, "mathematically perfect," by 1872.

1560s, in reference to a of Protestants that arose in 16th century England, originally generally, "opponent of Anglican hierarchy," later applied opprobriously to "person in the Church of England who seeks further reformation" (1570s), and thus to a member of any faith or sect or party that advocates purity of doctrine or practice (used of Muslims from 1610s). Probably formed from purity. As an adjective from 1580s.

What [William] Perkins, and the whole Puritan movement after him, sought was to replace the personal pride of birth and status with the professional's or craftsman's pride of doing one's best in one's particular calling. The good Christian society needs the best of kings, magistrates, and citizens. Perkins most emphasized the work ethic from Genesis: "In the swaete of thy browe shalt thou eate thy breade." [E. Digby Baltzell, "Puritan Boston and Quaker Philadelphia," 1979]

In its original sense, the word was largely historical from 19c.; the extended use in reference to anyone deemed overly strict in matters of religion and morals is from 1590s. The original Puritans developed into a political party in the reign of Charles I and gradually gained the ascendancy but lost it on Cromwell's death. During their early struggles many settled in Massachusetts.