One of the biggest problems for Protestantism to spread in Spain (iirc there were two Lutheran tiny minorities in Seville and Valladolid but were quickly destroyed) was that the Spanish Church, thanks to the reforms of the Cardinal Ximenez Cisneros had by the time that Charles I/V arrived, gone through its own sort of Counter-Reformation.
Many of the ideas that were later applied by the Counter-Reformation were introduced in Spain in the late 15th, early 16th century so it's difficult to have Protestantism when the main grievances against Catholicism had been reduced by forcing monks and priests to less ridiculous practices as those in other places.
Obviously the use of the Spanish Church by the Crown (for example, until 1977, the Spanish Monarch had the right to name the Spanish bishops) as another element to ensure social, religious and political homogeneity and conformity with the political system makes very difficult for the Crown to change their policy. They had all the influence in and through the Church they could need.
Also, the spirit of the Reconquista ensured that the basis of the Spanish proto-national sentiment was not based on speaking a common language or hating x European country, but rather on being Christian, and in Spain, being Christian has always been (even today) been synonymous with being Catholic.
Many of the ideas that were later applied by the Counter-Reformation were introduced in Spain in the late 15th, early 16th century so it's difficult to have Protestantism when the main grievances against Catholicism had been reduced by forcing monks and priests to less ridiculous practices as those in other places.
Obviously the use of the Spanish Church by the Crown (for example, until 1977, the Spanish Monarch had the right to name the Spanish bishops) as another element to ensure social, religious and political homogeneity and conformity with the political system makes very difficult for the Crown to change their policy. They had all the influence in and through the Church they could need.
Also, the spirit of the Reconquista ensured that the basis of the Spanish proto-national sentiment was not based on speaking a common language or hating x European country, but rather on being Christian, and in Spain, being Christian has always been (even today) been synonymous with being Catholic.