The scripture you quote shows that there were divisions amongst Christians circa A.D. 55, as existing divisions prompted Paul to write that admonition. He goes on to mention the risk of sectarian splits with some following Paul, Apollos or Cephas. Others wisely said they followed Christ. In chapter 3 Paul speaks again of jealousy and quarrelling and factions, then in chapter 5 he exposes gross immorality in their midst. Yet, despites those disagreements, the first century Christian Church existed. The same could be said of the newly Reformed Church in the 16th century. It existed despite disagreements and sectarian splits and immorality. But your question is about ‘consensus’ regarding Reformed doctrine; you want to know how it was arrived at.
Let me quote the start of the book ‘The Reformation’ by Owen Chadwick (Vol. 3 of The Pelican History of the Church, 1979 edition)
“At the beginning of the sixteenth century everyone that mattered in
the Western Church was crying out for reformation. For a century and
more Western Europe had sought for reform of the Church ‘in head and
members’ and had failed to find it. If you asked people what they
meant when they said that the Church was in need of reform, they would
not have found it easy to agree.” Page 11
It can safely be said that the Reformation began despite disagreements as to what, exactly, needed to be reformed, and how. We know that Martin Luther’s 95 Theses lit the touch-paper that caused an explosive result, with reverberations down to this day. Yet, bear in mind the extent of doctrinal issues therein, compared with other matters. Quoting again from Chadwick:
“When churchmen spoke of reformation, they were almost always thinking
of administrative, legal, or moral reformation ; hardly ever of
doctrinal reformation. They did not suppose the Pope’s doctrine to be
erroneous.” Page 13 “The Ninety-Five Theses contained no mention of
the doctrine of justification by faith. But in spite of the silence of
the theses, [Luther’s] attack upon indulgences sprang out of ‘my
theology’, out of a Pauline conviction of God’s grace. The Indulgence
he believed to be pernicious because it was misleading simple souls.
He saw it as an external and damnable symptom of so much that was
inwardly wrong with the Christian teaching of his generation, a
teaching which asserted or suggested that God could be placated by
external acts, by forms, by payments, by ‘good works’. Luther did not
attack indulgences and thereby reach a doctrine of justification by
faith alone. He applied an already appropriated doctrine of
justification to judge a particular indulgence.” Pages 46-47
I mention all this because herein lies the understanding of what role ‘consensus’ played both in the Church in Corinth, and in the Reformation. When it is clearly seen that something is very wrong in the Church, the need is not to get everyone round a table to agree to changes in administration, or to vote different people in to office, or to produce a list of doctrines from which to form some Creed or other. The need is to identify from Scripture alone the principles that are being violated by the Church, then to lay the axe to the root of that problem. It’s no use trimming the shrubs if they are still hiding the root of the problem. When Luther nailed that paper to the door, it was the first nail in the coffin lid of a corrupt church system. It wasn’t a theological treatise. Theology got thrashed out later.
Huldreich Zwingli, the reformer of Zurich wrote “Commentary on True and False Religion” (1528), a systematic theology with impact. He rejected much of Catholicism, Lutheranism and Anabaptism. (Luther also turned against Anabaptism.) But Calvin’s “Institutes” formed a general consensus. He died in 1564.
By the time the Reformation really got going, the consensus was not about church systems or secondary matters that Paul identified as “disputable” (Romans 14:1) – it was based on a rediscovery of the power of the unadulterated word of God, that was now being translated into the vernacular and put in the hands of ordinary folk in printed form. And that is what needs to be rediscovered today in Protestantism.
“Always Reforming” is the motto many Protestants are supposed to go by. Yet Reformed Christians keep hiding in their comfort zones, not even looking at the modern issues that are corrupting the Church today. How many see the “external and damnable symptoms of so much that [is] inwardly wrong with the Christian teaching of [our] generation”?
The basics of essential Christian doctrine have a large consensus amongst Protestants. But the need is to live them out in everyday life and in society, showing to a godless world the transforming power of the word of God in believers’ lives. It’s not “contradictory denominations” that is the problem today, but “contradictory living” by those who claim to be “Reformed” but whose profession could be doubted on the basis of their worldliness and their love of church systems. The need is to promote the biblical gospel, and to live it. “Come back, Luther! All is forgiven!”