Last month I posted a link to Mark Shea's article "In Essential Things: Unity". The second article in that series is titled "In Doubtful Things: Liberty". The final article is titled, "In All Things: Charity".
In the second article, Shea shows how the Catholic Church encourages and protects diversity. That might come as a surprise to those who frequently refer to the diversity of beliefs in the Catholic Church as evidence that sacramental magisterial authority is not the solution to the fragmentation of denominationalism. But we must not confuse division with diversity. Being in schism is a sin. But diversity within the Church reveals in various ways the manifold beauty and perfection of the Blessed Trinity. Shea's point in that second article is that one way of damaging the unity of the Church is to treat as essential something that is in actuality not essential.
So this raises a question: Whose decision regarding what is (and what isn't) essential is authoritative? If the answer is "No one's", the result would be absolute chaos. But from the days of the Apostles, the answer to this question has always been "Those who were so authorized by the laying on of hands by those who were authorized by Christ." The Church has always believed and taught that only the bishops in sacramental succession from the Apostles have the authority to determine what is essential. That belief and practice was rejected by the Protestants. And that is one of the primary reasons why Protestantism has fragmented into so many denominations.
"Let unity, the greatest good of all goods, be your preoccupation." - St. Ignatius of Antioch (Letter to St. Polycarp)