What do you understand about these verses without any mental gymnastics?
So essentially keep my answers brief and direct. That's probably best and I'll do my best. Still, far easier to ask brief questions than it is to give brief replies.
and how do you think the early Christians understood it?
I believe there was turmoil and disagreement and given we eventually landed in the reformation period we know this was the case.
Still, we can look at the council of nicea as an example of early turmoil in early organized church. Most people say that Nicea was where "the church invented the bible" or "the church invented the trinity". Not correct.
For approximately 3 centuries prior to 325 AD Christians were severely persecuted for the scriptural doctrine of the Trinity they taught. They didn't use the term "Trinity" as it was later coined, but they absolutely discussed the coequal, coeternal persons of God in the Father, Son and Holy Spirit.
In the decade or so leading up to the Council of Nicea a presbyter named Arius spoke out against his church bishop and made the claim that Jesus, although on earth to fulfill a divine purpose, was in fact created by God and was therefore neither eternal nor was he deity.
After several years of this opposing position being taught by Arius, it eventually reached Emporer Constantine's ears and he feared that this teaching would eventually split the Christian church that was enjoying a breif period of peace from all out persecution. That said, he convened 300 bishops to appear at a council in Nicea on June 19, 325 AD to discuss Arius' competing idea of Jesus' being created by God. The council convened and discussed the point and despite Arius' "silver tongue" he was unable to convince the vast majority of his position given the existing teachings of the father, son and spirit dating all the way back to Christ himself.
That said, the trinity was not created in Nicea, but was merely upheld and reaffirmed there. I'll concede the concept may have been coined under the umbrella term of "Trinity" at this point, but the council certainly did not create the theology there...that's a twisted myth. In the years that followed, Arius' small group of believers eventually succumbed to infighting within their ranks and his unorthodox teachings fell to the wayside for the most part; although, today some small groups of "Christians" still deny the Trinity.
Here is an example of early Christian infighting that was resolved via council.
"For my flesh is meat indeed: and my blood is drink indeed"
"Therefore, whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord."
Keeping everything brief and general, I do not abide by the RC doctrine of transubstantiation. I think the RCC’s exigesis of this scripture is a gross misinterpretation. Keeping it very simple, the Lord works in signs and covenant symbols throughout scripture. This passage in John 6 is no different and the interpretation is not meant to be literal….it’s a spiritual concept.
For example, Christ also referred to himself as the vine and his followers as fruit bearing branches. Does he literally become a vine and we literally sprout oranges and apples from ourselves? Of course not. In the OT in Exodus the Lord says that he delivered the Israelites out of their slavery on the wings of eagles. Do we believe that God sent countless eagles to place the enslaved Israelites on their wings and fly them out of Egypt? Again, of course not.
As Christ further states within John 6:
“It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life.”
Further, I believe the RCC concept ignores the greater context of the immediate passage and associated scripture outside of it. As it states in Isaiah we are to understand these theological concepts in scripture "precept upon precept".....the ideas build upon one another and are rarely isolated extractions with no context.
Remember, "a text without a context is always a pretext".
"And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it."
In order to again be brief I'll simply note the following:
Within the greek translation of this verse there isn't a definitive understanding of the use of the word "rock"......"petros" in reference to Peter (a movable rocky structure) as opposed to the more common "petra" used as a bedrock type foundation and in this case the foundation of the church. Peter cannot be both "petros" and "petra", but certainly he is the chief apostle. I actually believe that this is also just clever verbage used by Christ, but that's my humble opinion.
I would also say that scripture refers to Christ as the cornerstone (in OT scripture in Isaiah and NT scripture in Ephesians), Paul's letter to the church at Corinth states there is no other foundation other than Christ and that Christ is the rock and in Peter's NT writing he also affirms Christ as the rock.
Do I believe this scripture establishes the papacy and Peter as the first infallable Pope? No. I believe the only infallible words of Peter were those inspired by God that he penned in NT scripture. Beyond that the foundation of the church is Christ alone.
None of this is new argumentation and none of it is posted with anger and I welcome other viewpoints because I don't claim mine as absolute or infallible.