When Martin Luther nailed his protests against the Pope to the Wittenburg church door he began a chain of events that no one would have ever predicted. The monk had read the gospel of St Paul very closely and found two teachings in there that challenged Roman Christianity directly. There were many points he made in his protest: nearly one hundred, but the major principles were that no man could stand between man and his maker and also that Natural born leaders are there because it is divined by God. A picture depicting the Pope with his feet being washed alongside a picture of Jesus washing his desciple's feet, brought the message home clearly to the masses.
The German princes adopted the new concepts that have now become known as Protestantism but was then the start of a movement to force the Pope to change his ways and adapt his church. The movement became a political one when the German princes displayed their divine leadership and took papal lands. The Pope responded by sending Imperial armies from Catholic states and countries, to crush the German princes.
In Bohemia, the Catholic leaders were booted out by the people and Charles' sister and her husband became the monarchs as elected by the people. Elizabeth became known as the 'Winter Queen' because she lasted only one winter. The Pope financed a major military campaign that resulted in the successful defeat of the protestants at White Mountain (which also marked the beginning of the 30 years' war). The protestant caused struggled against papal armies for years until the Swedish King Gustavus Adolphus strung together several successfull military campaigns and converted many to Protestantism.
Henry VIII had converted to Lutheranism when the Pope had denied him a divorce. Many see this simplistically but it was inextricably linked to the principles of Lutheranism that Henry was a divine leader chosen by God and no man can stand between man and his God. The Pope really had no say in the matter when Lutheranism was invoked. England became protestant with the King and the Bishops in place, not standing between man and his maker, but as divine leaders elected by God to lead the people.
All went well until the Swiss developed their own type of Protestantism. Something Luther would never have approved of. Calvin led a new theology based on Luther's original Wittenburgh protest. Calvin could not accept the two teachings that seemed to him to contrast. He could not accept that 'Princes' were divined by God. He saw them as yet another way to put someone before man and his maker. This paved the way for a challenge against any authority and could undermine whole social structures. Calvinist ideas infiltrated society at all levels but took hold of Scotland in particular. Unhappy with rule from England this challenge to leadership with a religious precept, fostered the Solemn league and covenant and a rejection of Bishops and a challenge to the Kings rule. Some in England, known as the Godly or Puritans, arrested the principle of Calvinism too. Since Henry's time the puritans had been a manageable minority but when the Scots openly challenged Charles's authority in the bishop's war, and the Queen openly flaunted Roman Catholicism, considering her raison d'etre to be to convert the English to Catholicism, the English felt threatened. bloody Mary's return to Catholicism and the gun powder plot were fresh in the English people's minds. If the King, as part of the Lutheran principles, could not protect the people from the Catholics they would have to do it themselves. To take that action, they had to embrace the principles of Calvinism, in England it was known as Puritanism. Not all were Puritans however, and some simply wanted to save their natural leader from his 'evil' councillors: they remained Lutherans.
Charles' adherence to Lutheran principles, the foundation of the Church of England, is seen in modern eyes as simple stubborness and a tyrannical adherence to divine leadership. Charles had no choice about that, he was, to the core, a Lutheran as was lawfully built in to the English Church. He maintained the principles of the Church of England until his death and could have, at any time 'abandon the church' as his Queen had instructed him. In the restoration we see the re-establishment of Lutheranism in our country and the rejection of those adhering to Calvinist principles. Many of whom went to America.
So why did Charles not convert to Catholicism and take the Pope up on the offer of money and armies to reduce his kingdom? Is it because he made a vow to uphold the Church of England at his coronation and that he was a man of principle or is it that he feared anarchy if he were to accept that people could be leaderless? Did he feel personally threatened, he was a king by default since his brother had died, and he was a small stuttering man? Or was it that he feared that a division in the Protestant church would invite another bloody Roman Catholic reign such as that of bloody Mary. We will never know exactly why but we do know he did the right thing all the way up to his death. He stood by the principles of the Church of England established by Henry VIII and defended miraculously by Elizabeth, and firmly rooted in the the Gospel of Paul as espoused by Martin Luther. He is exonerated by the return of the church and its laws on restoration of the monarchy.