There is a belief among the Protestant believers that as long as someone declares that “Jesus is Lord” they are part of “The Church” the “Body of Christ”. There’s no real common doctrine and no real historical roots tying the modern evangelicals to the Apostles. 

The Church that Jesus built was founded on the confession of the Apostles that “Jesus is the Christ, the Son of God” and he only referred to ONE Church. That Church was a defined entity, a group of people, yes, not a specific building, but definitely a physical organism that PEOPLE could find. God knows the heart so HE doesn’t need a physical description to find the Church. MAN needs the Church, not an organization per se but a physical entity with definitions of what makes up the Church. How does anyone know what the Church is? What does the Church believe? What of Salvation? Is Salvation only available through the Church? Are we able to know about all these other groups that call themselves Christians?
Well, let’s first realize that the Church existed for 356 years before there was a defined New Testament to refer to. There were books and letters that were shared and read in the Church, but there wasn’t a collection like we have today that people knew was Holy Scripture. That itself made it necessary for the Church to make some definitions, list parameters of what a Christian is. At the time, early fourth century, there was a preacher that was traveling around preaching something different. He was preaching that Jesus, being begotten of the Father, was a created being. If that were true then Jesus couldn’t be God. 

After considering the input from all the teachers and bishops of the Church, the first part of the Creed was composed. It defined the belief about the Father and the Son. The first council of the Church closed with instructions to take this Creed and make certain that everyone in the Church was aware of and agreed to it. This was so that everyone in the local churches spoke the same, believed the same, and communicated it abroad. 

A couple of decades past when someone began trying to teach about the Holy Spirit. The exact teaching is unimportant to this current discussion but the solution was another council where the leaders of the Church gathered again. They considered carefully all the teachings and once again identified the teaching that was correct and common among the local churches. They then composed the completion of the Creed. 

Now they had a defined list of teachings, passed down from the Apostles, taught across the known world by the local churches, defining the Christian Church. This completed Creed now was prescribed to be read and recited and taught to everyone in the Church. It was not optional, if someone was to be part of the Church, THIS was the belief that they must hold. To do anything else was to be outside the Church. 

In the Creed, there was the definition of the Church, that there was ONE Church. Yes it was made up of many local churches but they all believed the same thing, that was defined in the Creed. 

The Church was HOLY. The people being made Holy, sanctified by God, set apart by God, the Church was HOLY. 
The Church was CATHOLIC. Today many recoil from that word but there is nothing connecting the word “catholic” in the Creed and the group that today call themselves the Roman Catholic Church. That individual group divided itself from the Church in 1054ad and bears little resemblance to or even the same doctrine to the original. The word “catholic” means universal. It was to clarify that the Church and her doctrine applied to anyone in any land. No culture was unable to receive forgiveness and redemption in Christ. The teachings of the Church would not exclude anyone who repented and wanted forgiveness. Jesus had overcome death by death and anyone who willingly came to Him could be received into the Church. 
The Church was defined as APOSTOLIC. The Church foundation was the testimony of the Apostles. Jesus had told the Apostles that he would build his Church and that the “Gates of Hades” would not prevail against the Church. 

So now the Church had a defined description of what she believed. This was a foundational document. It was not until eight years later that Church Leaders collected a catalog of the books contained in the New Testament and began publishing that to the local churches. To be clear, without the Creed in its original form, calling oneself a Christian is a false statement. 
So we have, within the Creed the specific definition of a Christian. We have a definition of the Church, ONE HOLY CATHOLIC AND APOSTOLIC CHURCH. A single entity, visibly definable, (ONE) a church that is sanctified, set apart by God (HOLY) a church that is universally applicable, it fits into any country or culture (CATHOLIC) and it is founded on the testimony of the Apostles (APOSTOLIC). 

Now, fast forward to today. Some people have many different definitions of a Christian. Interesting we also have many in the heterodox community, the many teachings of the Protestant or evangelical religions, who first cling to the teaching known as Sola Scriptura or Scripture Alone. This teaching originated with Martin Luther. He was an interesting study, a Roman Catholic Priest that wanted to reform Rome. He translated the Scriptures into German for his followers in Germany. He actually got to decide what books he would include in his Bible, and he even chose how some words and phrases were translated that fit into his doctrinal statements. So he came up with this idea that ONLY scripture could be used for Doctrine but there’s no place in the Holy Scriptures that this teaching is taught. 

Today we have many different groups that call themselves “Christians” without definition. If you are with them long enough you can find out that each individual is their own church. They each are the leader of their own religion. They each take a verse or a passage and they read it and then THEY decide what “God is saying TO ME” in that passage. Each person is like the Roman Pope, they just decide that they speak for God. There is no authority, no community that can decide, each person is his own arbiter of what God says.  

So what do we have? We have 30,000-50,000 churches in the USA and each person in those churches is deciding for himself or herself what God is saying. Then they are joining together only because they might agree on some points that the group thinks is important. They “fellowship” with other groups around holidays or other special events because, even though these others don’t agree on the “important” Doctrine they DO declare that Jesus is Lord. As long as they do that, we are able to worship together. 

If the Church is truly a single entity, should it speak the same in whatever group I find it? If it is founded on the testimony of the Apostles, following the Apostles teaching, won’t that teaching be universal? If as we are able to read, the Church is the “body of Christ” then how is it that Joe can leave this church he grew up in, move down the street and found a NEW church and BOTH of them be the “Body of Christ”?

Well I have presented many questions that need to be tied together. The New Testament was canonized, meaning the table of contents was finally decided in 389ad. The Church had begun in 33ad and had spread out over much of the known world. The Church had passed all teachings down both verbally and in written form for 356 years before beginning to get the New Testament disseminated to all the people. When the New Testament was disseminated the Church began to interpret scripture in the life and Liturgy of the Church. The teachings in the Church were already there, the icons, the stories and how to interpret these truths was already part of the Church. This made it a simple idea, a logical or reasonable plan to interpret the Holy Scriptures through the “Lens” if you will, of the life of the Church. 

So within the Ancient Church we see that the biggest reason that each person was not defining what God was saying is the simple truth that the life and Liturgy of the Church was the lens by which everyone read and understood the Holy Scriptures. 

If we could all define God our own way, as is common with heterodox religions, then Christianity would be nothing more than a different form of Hinduism where each person has his own god and everything is equal. With that in mind there would be no real reason to attend ANY Church. There’s nothing sacred, nothing of importance and if one doesn’t attend there’s no consequences. However, the Church is diminished by loss of community. There is no strength unless it is a community, (Jesus and US, not Jesus and ME). That is what was always understood by St. Paul’s encouragement that we not neglect the gathering together. We need the community the communion of the people from the common cup where the Body and Blood of Christ is granted to us and He abides in us as he promised and we then can abide in him.