Leanda de Lisle writes brilliantly in an article for History Today about the reign of Charles I, particularly its religious context:
Henry VIII’s nationalised form of Anglo-Catholicism did not survive him. From the reign of Edward VI, English Protestants saw the Church of England as part of international Reform Protestantism – a stripped-down Protestantism that would later be labelled Calvinism – just as Scottish Protestants did their Presbyterian kirk. The fate of British Protestantism was linked to what happened to their fellow Calvinists in Europe; there, Protestantism was in retreat. In the 1590s, Protestants held half the land area in Europe. A century later they would hold only a fifth.
Anxiety over Calvinist survival on the continent gave an edge to concerns at home about the half-reformed nature of the Church of England, with its episcopate (government by bishops) and other pre-Reformation hangovers. There was mistrust of Stuart enthusiasm for Elizabethan compromises, particularly among those labelled Puritans.
Protestantism had only survived where it had been imposed or permitted by rulers. To defend themselves, British Protestants had therefore developed ‘resistance’ theories, arguing that kings took their authority from the people, who had the right to overthrow any monarch of the ‘wrong’ religion, which included being the ‘wrong’ kind of Protestant. ‘Popery’ was the term applied to those who sought to spread Counter-Reformation; it was also applied to any reversal of Calvinism.