How did monarchs in Spain, France & England use religion to solidify their power?This is during time period of 1500-1700.
There's probably a specific answer to this question to be found in your textbook and you should check for that. People do not always emphasize the same things so my answer may not be exactly what your book says.
I would argue that religion was used in two ways. First of all, it was used to enforce the rules in the societies. If the monarchs were on the side of the Church, they had the force of God behind them and could use it to give them more power. In other words, it was another way to make their people obey them.
Second, they used religion as a rallying point for wars against one another. The Spanish and the English hated each other in part because of their religious differences.
They used it openly and freely, in my opinion. The Catholic Church at that time, for example, adopted religious beliefs, interpretations and practices that were most likely to generate loyalty among the people at large, and to make it easier for government to exert control over them.
The Church was used as a vehicle for tax collection (thought it wasn't often called "taxes"), for social direction and control, and for the centralization of authority.
The Church of England, once it developed into a dominating force, became hopelessly intertwined with government authority and control.
During the 16th century the Catholic Church was all powerful all over Europe. However, with the Reformation its power and authority came to be challenged.The century following the Protestant Revolution was a gruesome one in Europe. Catholics and Protestants were constantly at odds. People were disemboweled, hung, and burned for practicing their chosen religion.
In England Mary I (18 February 1516 – 17 November 1558) was the eldest daughter of the Protestant, Tudor King Henry VIII. On ascending the throne she quickly restored Roman Catholicism in England. She was nicknamed "Bloody Mary" because she persecuted the Protestants and burnt many of them at the stake.
Similarly, King Charles I [1600-1649] who married a Catholic Princess and had Catholic sympathies was executed by the Puritans led by Oliver Cromwell after a bloody Civil War.
Oliver Cromwell [1599-1658] himself rigorously enforced Puritanism during his rule.