Note: Calvinism [John Calvin] for all practical purposes has taken the three tenets of the Protestant Reformation (Sola Scriptura , Sola Fide and Sola Sacerdo – the Believer’s Priesthood) and has reduced it to the two tenets of the Calvinistic faith (Sola Scriptura and Sola Fide) virtually removing the Sola Sacerdo – the Believer’s Priesthood from the Reformation and in doing so replacing the authority of the common Christian [Believer’s Priesthood] with an elite Presbyterian class of priesthood.
Source: Theopedia.com
The theology of the Reformers departed from the Roman Catholic Church primarily on the basis of three great principles:
Sola Scriptura (by Scripture alone) was one of the watchwords of the Reformation. This doctrine maintains that Scripture, as contained in the Bible, is the only authority for the Christian in matters of faith, life and conduct. The teachings and traditions of the church are to be completely subordinate to the Scriptures. Roman Catholicism, on the other hand, holds Scripture and Tradition to be of the same inspired Deposit of Faith.
Sola Fide (by faith alone) was the other watchword of the Reformation. This doctrine maintains that we are justified before God (and thus saved) by faith alone, not by anything we do, not by anything the church does for us, and not by faith plus anything else. It was also recognized by the early Reformers that Sola Fide is not rightly understood until it is seen as anchored in the broader principle of Sola Gratia, by grace alone. Hence the Reformers were calling the church back to the basic teaching of Scripture where the apostle Paul states that we are “saved by grace through faith and that not of ourselves, it is the gift of God,” Eph. 2:8.
The third great principle of the Reformation was the priesthood of all believers. The Scriptures teach that believers are a “holy priesthood,” 1 Pet. 2:5. All believers are priests before God through our great high priest Jesus Christ. “There is one God and one mediator between God and man, the man Christ Jesus,” 1 Tim. 2:5. As believers, we all have direct access to God through Christ, there is no necessity for an earthly mediator. The Roman Catholic and Eastern Orthodox concept of the priesthood was seen as having no warrant in Scripture, viewed as a perversion and mis-application of the Old Testament Aaronic or Levitical priesthood which was clearly fulfilled in Christ and done away with by the New Testament.
As a result of these principles, the Reformers rejected the authority of the Pope, the merit of good works, indulgences, the mediation of Mary and the Saints, all but the two sacraments instituted by Christ (Baptism and the Lord’s Supper), the doctrine of transubstantiation, the mass as a sacrifice, purgatory, prayers for the dead, confessions to a priest, the use of Latin in the services, and all the paraphernalia that expressed these ideas.
Even though the Roman Catholic and Eastern Orthodox churches fall within Orthodoxy as most would define it, much of their teaching beyond the basic tenets is regarded as erroneous by conservative Protestants. In fact, they would say much of it is clearly to be regarded as false teaching which has perverted the gospel of God’s grace in Jesus Christ. In general, evangelical Protestants see the Reformation as simply a call back to biblical Christianity.
John Calvin (1509–64) — Calvin was a French theologian and reformer who fled religious persecution in France and settled in Geneva in 1536. He instituted a form of Church government in Geneva which has become known as the Presbyterian church. He insisted on reforms including: the congregational singing of the Psalms as part of church worship, the teaching of a catechism and confession of faith to children, and the enforcement of a strict moral discipline in the community by the pastors and members of the church. Geneva was, under Calvin, essentially a theocracy.
Basic Christian Wiki: Holiness – Calvinism
Why We No Longer Call Ourselves “Reformed” or “Calvinists” Sovereign Redeemer Assembly