let's crack into ephesians 4:1-7
"1Therefore I, the prisoner of the Lord, implore you to walk in a manner worthy of the calling with which you have been called,"
What calling? the call to faith. THE CALL. not a call, a church, a belief.
2with all humility and gentleness, with patience, showing tolerance for one another in love,
though the reformation was not a time of tolerance generally, there were some that were. John Calvin was generally tolerant. Servetus, despite popular belief, was given many responses, 30 or so, in correspondence to his non-trinitarian heresy. we call that heresy because the bible teaches it, not because its in a creed. and John Calvin clearly warned him not to come to Geneva. This is about the most intense thing you can lay on the man.
Luther has a much bigger rap sheet.
3being diligent to preserve the unity of the Spirit in the bond of peace. 4There is one body and one Spirit, just as also you were called in one hope of your calling; 5one Lord, one faith, one baptism, 6one God and Father of all who is over all and through all and in all.
The faith is one. There is one God here, and one way of understanding the scriptures: not through the "holy mother church". While Luther may very well have been talking about reforming the church, it was a matter of sola scriptura. not creeds. not councils. He was an Augustinian doctor of the church and was bent on putting scripture first.
7But to each one of us grace was given according to the measure of Christ’s gift.
We were all saved by the singular God of this singular faith and church, through his singular spirit, 3 persons, one God. and we are all to seek, in one way or another, to harmonize and get down to the truth. And we've all been given a measure of grace to believe the true gospel and follow it, some more, some less.
The reformation was the birth of Lutheranism, Calvinism, Arminianism, and all their offshoots. these three wings of faith are very close depending on which topic we're talking about, and all these backgrounds are valid forms of faith. all of them agree on God in the basics.
So a heretic is someone who is an anti-christ. a person who does not accept the plain revelation of scripture and the God of scripture. They twist and contort the bible to their own ends.
Now, THE EARLY CHURCH was in no way perfect. we had a few extra books floating around, the theologians had their rough edges but by and by, the pauline theological position that the reformers sought to reclaim -again, not just because of creeds- was greatly diminished, and people who tried to believe according to orthodox scripture were branded heretics and burned at the stake. the scarlet whore of babylon had reigned for a time.
But God, even in that pagan age, produced scholars who regarded the scripture and loved the Lord, and they preserved the bible more than adequately. The bible has been handed down as it was from 2000 years ago, in the original greek and hebrew and aramaic. An act of God for sure.
The reformation was a great time of revival for christians because never before have we had our bibles in the common tongue. never before had we been given freedom to read the scriptures for ourselves. If it were not for them, there would be no witness lee movement, no assemblies of god, no southern baptist church... the majority of the world would still believe in heresy.
And make no mistake, just because the catholic church believes certain core values of christian faith does not make the institution any less heretical. "vicar of christ" "perpetual virginity of mary" "purgatory" "indulgences" "confession" "penance". the institution is heresy. people in the church may still be in faith, its possible to be deceived and be saved to a certain extent, but if the plain truth of scripture is there and being rejected those people will be held accountable.
The aim of the reformation was not ONLY to bring the catholic church to sound teaching because of the burden as mentioned in ephesians, but to make scriptural, sound theology the dictator of how we run the church.
John Calvin, in my opinion, was the most faithful man of the reformation. His church was not merely an overhaul, it was a schism. 2 sacraments, both symbolic, 3 biblical leaders; the lead-elder or pastor, elder, and deacon. no funny clothes or funny prayers or traditions of men (with the exception, also in my opinion, of the continued paedobaptism)
http://www.1689.com/confession.html
the 1689 particular baptist confession is neither catholic, nor appealing to catholics to change. it is not based in traditions of men, nor of creed worship. It is the plain, scriptural statements of faith as set forth by the holy scriptures. In my opinion, it is the most faithful and specific creed of the protestant era.
the westminster confession is like it, but less specific
the heidelberg catechism was made for children to understand, so is generally faithful
and many more. the reformation was not pandering to catholics, it was pleading with a sinful institution to repent. it did not, therefore, protestantism. and any good church ought to have one bible, and only that bible, for forming all of its practices and regulations.