Fourth-century reformation
Sixteenth-century reformations
The Reformation of Luther and Chemnitz
The Reformation of Zwingli and Calvin
The Radical Reformation
The Counter Reformation
The reformation of the fourth century
The Athanasian Reformation
At a time when the church had declined to the point that the consensus of bishops tolerated the teachings of Arius, Athanasius led the reform back to the apostolic faith confessed in the Council of Nicea.
The Athanasian Creed
Far from finding its basis in any human tradition, the Athanasian Creed presents the one true faith, the mystery of the good news of Christ, according to what has "been revealed to his holy apostles and prophets by the Spirit" (Ephesians 2:5):
Whoever wished to be saved must, above all else, hold the true Christian faith. Whoever does not keep it whole and undefiled will without doubt perish for eternity. This is the true Christian faith, that we worship one God in three persons and three persons in one God without confusing the persons or dividing the divine substance. For the Father is one person, the Son is another, and the Holy Spirit is still another, but there is one Godhead of the Father and of the Son and of the Holy Spirit, equal in glory and coequal in majesty. What the Father is, that is the Son and that is the Holy Spirit: the Father is uncreated, the Son is uncreated, the Holy Spirit is uncreated; the Father is unlimited, the Son is unlimited, the Holy Spirit is unlimited; the Father is eternal, the Son is eternal, the Holy Spirit is eternal; and yet there are not three eternals, but one eternal, just as there are not three who are uncreated and who are unlimited, but there is one who is uncreated and unlimited. Likewise the Father is almighty, the Son is almighty, the Holy Spirit is almighty, and yet there are not three who are almighty but there is one who is almighty. So the Father is God, the Son is God, the Holy Spirit is God and yet there are not three Gods but one God. So the Father is Lord, the Son is Lord, the Holy Spirit is Lord, and yet there are not three Lords but one Lord. For just as we are compelled by Christian truth to acknowledge each person by himself to be God and Lord so we are forbidden by the Christian religion to say that there are three Gods or three Lords. The Father was neither made nor created nor begotten by anybody. The Son was not made or created, but was begotten by the Father. The Holy Spirit was not made or created or begotten, but proceeds from the Father and the Son. Accordingly there is one Father and not three Fathers, one Son and not three Sons, one Holy Spirit and not three Holy Spirits. And among these three persons none is before or after another, none is greater or less than another, but all three persons are coequal and coeternal, and accordingly, as has been stated above, three persons are to be worshiped in one Godhead and one God is to be worshiped in three persons. Whoever wished to be saved must think thus about the Trinity. It is also necessary for eternal salvation that one faithfully believe that our Lord Jesus Christ became man, for this is the right faith, that we believe and confess that our Lord Jesus Christ, the Son of God, is at once God and man: he is God, begotten before the ages of the substance of the Father, and he is man, born in the world of the substance of his mother, perfect God and perfect man, with reasonable soul and human flesh, equal to the Father with respect to his Godhead and inferior to the Father with respect to his manhood. Although he is God and man, he is not two Christs but one Christ: one, that is to say, not by changing the Godhead into flesh but by taking on the humanity into God, one, indeed, not by confusion of substance but by unity in one person. For just as the reasonable soul and the flesh are one man, so God and man are one Christ, who suffered for our salvation, descended into hell, rose from the dead, ascended into heaven, is seated on the right hand of the Father, whence he shall come to judge the living and the dead. At his coming all men shall rise with their bodies and give an account of their own deeds. Those who have done good will enter eternal life, and those who have done evil will go into everlasting fire. This is the true Christian faith. Unless a man believes this firmly and faithfully, he cannot be saved.
From Tappert, T. G. (2000, c1959). The Book of Concord: The Confessions of the Evangelical Lutheran Church (The Three Universal or Ecumenical Creeds: III, 1-40). Philadelphia: Fortress Press. Spelling corrected.
Four reformations of the sixteenth century
False teachings other than Arianism led to sixteenth-century divisions among professing Athanasians.
The Lutheran, Zwinglian, Radical, and Counter Reformations
1. The Reformation of Luther and Chemnitz
Martin Luther did not create a new church, but returned to the holy universal church's creedal belief ''in the forgiveness of sins'': acquittal before God on the merit of Christ alone, through faith alone, to the glory of God alone. This Reformation recovered the doctrines of grace that had been affirmed a millennium earlier by the Council of Orange. The Lutheran confessions reject the changes made by the Zwinglian and Radical Reformations as fanatical, "enthusiastic" (hyper-spiritual) departures from the clear word of God. Thus, to classify traditional Lutherans along with fundamentalists and modem evangelicals as Protestant may betray an ignorance of church history.
The first such confession especially stressed continuity with the catholic church:
Requiring examination is the Lutheran claim "that nothing has been received among us, in doctrine or in ceremonies, that is contrary to Scripture or to the church catholic." The church is a norm of doctrine and more striking is the introduction to the abuse articles where the church, without reference to the Scriptures, is listed as norm: "Inasmuch as our churches dissent from the church catholic in no article of faith." The church as holy, catholic, and apostolic is certainly the depository of the truth, but churches and the catholic church in these references are to the historic, continuous communities of believers, whose doctrines and practices are accessible through the writings of Cyril, Leo, Augustine, Gerson, and others. Melanchthon challenges Rome's exclusivity, but not its claim to catholicity.
From Evangelical and Catholic: A Slogan in Search of a Definition 
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The understanding of the catholic church as confessed in Augsburg, quoted in part above, had to be defended against misunderstanding:
... the church catholic... is, rather, made up of men scattered throughout the world who agree on the Gospel and have the same Christ, the same Holy Spirit, and the same sacraments, whether they have the same human traditions or not.
From Tappert, T. G. (2000, c1959). The Book of Concord: The Confessions of the Evangelical Lutheran Church (Apology of the Augsburg Confession, Article 7). Philadelphia: Fortress Press.
Painting of Christ as preached by Luther
Why I believe the Lutheran Church This requires a PDF reader
2. The Reformation of Zwingli and Calvin
Zwingli and Calvin endeavored to more thoroughly reform the church in obedience to Scripture. Their line of thought became known as Reformed theology. This Swiss Reformation not only gave rise to innumerable denominations, including Baptist, Congregational, Presbyterian, and "nondenominational" sects, but also exerted a strong influence on the Anglican Church and consequently on its children Episcopalianism, Methodism, and Pentecostalism. Compared to the Lutheran Reformation, the Zwinglian Reformation radically distanced itself from the medieval catholic church:
The more recent concept of "Catholicism" as an antonym of "Protestantism" is a typical product of Reformed thought. The Lutheran Church... does not know to which side it belongs. For there are heresies in Protestantism which are just as dangerous as those of Catholicism. Lutheran theology differs from Reformed theology in that it lays great emphasis on the fact that the evangelical church is none other than the medieval Catholic Church purged of certain heresies and abuses. The Lutheran theologian acknowledges that he belongs to the same visible church to which Thomas Aquinas and Bernard of Clairvaux, Augustine and Tertullian, Athanasius and Ireneaus once belonged. The orthodox evangelical church is the legitimate continuation of the medieval Catholic Church, not the church of the Council of Trent and the Vatican Council which renounced evangelical truth when it rejected the Reformation.
For the orthodox evangelical church is really identical with the orthodox Catholic Church of all times. And just as the very nature of the Reformed Church emphasizes its strong opposition to the medieval church, so the very nature of the Lutheran Church requires it to go to the farthest possible limit in its insistence on its solidarity and identity with the Catholic Church.
From Sasse, H. (1979, original 1938). Here We Stand. Adelaide, South Australia: Lutheran Publishing House. pp. 110-111. Emphasis added.
3. The Radical Reformation
Anabaptists and others sought even more thorough reformation, seeing undesirable elements of catholicism in the above reformations. Heirs include the Amish, Mennonites, and Quakers.
4. The Counter Reformation
The Papacy responded to the "Protestant" Reformations by reforming many of its practices, but in the Council of Trent it anathematized the catholic teaching of justification by faith alone, thereby confirming the bishops' opposition to the Lutheran Reformation:
The Lutheran Church claims to be a Catholic Church in the strictest sense of the word: it acknowledges its identity with the orthodox church of all times and places... Since Rome drove the Evangelicals out of its fellowship, it was the Church of Rome which impaired catholicity and destroyed the unity of the church. What the Evangelicals demanded of the bishops... was no more than that the latter should not force them to sin against their consciences and thus to forsake the Gospel.
From Sasse, H. (1979, original 1938). Here We Stand. Adelaide, South Australia: Lutheran Publishing House. p. 90.
