Origin and history of qualify

1580s, "fitted by accomplishments or endowments;" 1590s, "affected by some degree of restriction or modification;" past-participle adjective from qualify (v.). By 1886 and into mid-20c. as a British English euphemism for bloody or damned.

To be competent is to have the natural abilities or the general training necessary for any given work ; to be qualified is to have, in addition to competency, a special training, enabling one to begin the work effectively and at once. He who is competent may or may not require time to become qualified; he who is not competent cannot become qualified, for it is not in him. [Century Dictionary]

c. 1300, qualite, "temperament, character, disposition," from Old French calite, qualite "quality, nature, characteristic" (12c., Modern French qualité), from Latin qualitatem (nominative qualitas) "a quality, property; nature, state, condition" (said [Tucker, etc.] to have been coined by Cicero to translate Greek poiotēs), from qualis "what kind of a" (from PIE root *kwo-, stem of relative and interrogative pronouns).

In early use, and for long thereafter, with awareness of the word's use in Aristotelian philosophy. From late 14c. as "an inherent attribute," also "degree of goodness or excellence." Meaning "social rank, position" is c. 1400, hence "nobility, gentry." From 1580s as "a distinguished and characteristic excellence." 

Noun phrase quality time "time spent giving undivided attention to another person to build a relationship" is recorded by 1977. Quality of life "degree to which a person is healthy and able to participate in or enjoy life events" is from 1943. Quality control "maintenance of desired quality in a manufactured product" is attested from 1935.