The old religion referred to here is the Catholic faith, and the new is Protestantism. The Protestant Reformation began as a movement to reform the Catholic Church. The leaders of the movement – including Martin Luther and John Calvin – believed that the Catholic Church had become corrupt. In 1517, Martin Luther attached a list of criticisms of the Church to the door of Castle Church in Wittenberg, Saxony. The list addressed doctrinal matters such as the sacraments, clerical celibacy, and the authority of the Pope, but Luther was particularly concerned over abuses in the selling of indulgences (official remissions of temporal punishment for sins).
In England, a series of events in the 16th century caused the Church of England to break from the Roman Catholic Church. At first the causes were more political than theological; in the past Henry VIII had even written a book defending the Catholic Church from Martin Luther’s accusations. However, when Henry wished to annul his marriage to his first wife Catherine of Aragon, the Pope would not allow it. Henry broke from the authority of the Pope and established himself as the head of the Church of England, giving himself power over doctrinal disputes, legal issues and the appointment of bishops. This break was not yet a true reformation, and the theology and practices of the new church were disputed for a long time afterwards.
More Protestant reforms were introduced during King Edward VI’s short reign, but in 1553 Mary Tudor came to power and sought a reunion with Rome. Under her rule, Protestant legislation was repealed and Protestants were executed for heresy.
When Elizabeth I ascended the throne she reintroduced (Protestant) Anglicanism as the official religion. She established herself as Supreme Governor of the Church of England and removed Catholic Councillors from the Privy Council. In 1558 the Act of Uniformity was passed, forcing people to attend service in an Anglican Church every Sunday. Many Catholics continued to attend Mass in secret, however. Puritanism, whose adherents shared the belief that the Protestant reforms had not gone far enough, began to emerge during Elizabeth’s reign.
It is in these confused times, after generations of religious upheaval, that this story is set. John Dee clearly favours Elizabeth and the Protestant faith. Bruno is a Catholic ex-friar, but he has been excommunicated for his radical ideas. He sees Elizabeth as a more enlightened ruler.