As noted in the introduction to my answer to
Why is there no archaeological evidence that Christians existed for 200 years after 70 AD? - Christianity Stack Exchange,
the "early church" refers to a period of several centuries that contains a long gap with little historical record.
The lack of evidence of early Christianity has been noted by many scholars.
Edward Gibbon, in The History of the Decline and Fall of the Roman Empire, said :"The scanty and suspicious materials of ecclesiastical history seldom enable us to dispel the dark cloud that hangs over the first age of the church.".
William Fitzgerald, in Lectures on Ecclesiastical History said: "Over this period of transition, which immediately succeeds upon the era properly called apostolic, great obscurity hangs ...".
Samuel G. Green in A Handbook of Church History said: "The thirty years which followed the close of the New Testament Canon and the destruction of Jerusalem are in truth the most obscure in the history of the Church. When we emerge in the second century we are, to a great extent, in a changed world.".
William J. McGlothlin, in The Course of Christian History said: "But Christianity itself had been in [the] process of transformation as it progressed and at the close of the period was in many respects quite different from the apostolic Christianity.".
Jesse Lyman Hurlbut, in _Story of the Christian Church, said:"For fifty years after Paul’s life, a curtain hangs over the Church, through which we vainly strive to look; and when at last it rises, about 129 A.D. with the writings of the earliest Church Fathers, we find a Church in many ways very different from that in the days of Peter and Paul.".
Other historians make similar comments about the lack of historical material from that period, and how, after a few centuries, suddenly Christianity is seen to be flourishing, with no evidence of how it got that way.
Whatever happened, it was not a smooth transition.
That long gap in the historic record separates the apostolic Church of God in Jerusalem and the Catholic Church in Rome.
The question, "Did any in the early church require a kosher diet?" will receive two very different answers, depending upon which side of the transition one considers.
The Apostolic Church of God:
TLDR: No one wrote about requiring a kosher diet for the same reason that no one wrote about forbidding murder and theft.
It was simply something that everyone took for granted, so there was no need to write about it.
The early church was entirely composed of Jews, so everyone naturally ate only kosher food.
Until Peter's vision (Acts 10 (NKJV)),
in which he is told that Christianity is intended for all mankind, "… God has shown me that I should not call any man common or unclean",
Christianity was entirely Jewish, the only difference being the belief that Jesus was the promised Messiah.
Christians and Jews lived, worked, worshiped, and studied together.
— from my answer to Were there implicit laws not referenced in the Acts 15 letter to gentile believers?
Arguments are continually presented by modern Christians that the Church described in the Bible did eat non-kosher food, but they are all examples of eisegesis (reading what one already believes into the scripture).
I won't discuss them here, but my answer to
Why do most Christians eat pork when Deuteronomy says not to?
refutes the most popular of these rationalizations:
- Initially, the prohibition against pork was part of the Law given to Moses [so it's binding only on Jews]
- Jesus declared all foods clean
- God told Peter that all meat was clean
- Peter said that nothing is unclean
- So let no one judge you in food or in drink
- It's only Old Testament
he Book of Acts records multiple instances of the apostles continuing to celebrate God's holy days, such as:
- Pentecost: 2:1, 20:16, 24:11, 1 Corinthians 16:87.
- Passover & Unleavened Bread: 12:3,4 20:6
- Day of Atonement: 27:9
- Unspecified: 18:20,21
- Sabbath: 13:14, 13:44, 16:13, 17:2, 18:4
Years after the Crucifixion, Peter claimed: "I have never eaten any thing that is common or unclean.".
Nowhere is there anything explicitly telling Christians to celebrate the holy days or to keep kosher.
There was no need, as everyone already knew that they should.
Following Peter's vision, Gentiles were welcomed into the Church, creating three problems.
Until this point everyone was Jewish and everyone was part of God's covenant with Israel.
(Historically, Gentiles did occasionally become Israelites, but they had to fully convert to Judaism.)
But what about new Gentile proselytes, would they have to become part of the "old" covenant too?
Many in the Church believed that this was true, that full conversion including circumcision was required.
Secondly, the transition from their previous Pagan lifestyle was quite extreme in some aspects
For instance many Pagans were vegetarians or ascetics, and some members of the Church were forcing them to eat meat or to enjoy life.
As a result, many potential converts were giving up because it was too much too soon.
Thirdly, those converts that had successfully adopted the Christian lifestyle were often shunned or ridiculed by their friends, families, and others in their previous life, and were in danger of lapsing back to their old lifestyle.
The Jerusalem Council resolved the first matter, saying that God's covenant with physical Israel was separate from God's covenant with spiritual Israel.
There was no need for Gentiles to convert to Judaism in order to become Christians.
They also decided that initially, proselytes need only obey those laws that Judaism teach God gave to all mankind:
The Seven Laws of Noah include prohibitions against worshipping idols, cursing God, murder, adultery and sexual immorality, theft, eating flesh torn from a living animal, as well as the obligation to establish courts of justice.
— Seven Laws of Noah - Wikipedia
…
Ignoring the four laws that almost all religions would consider obvious (blasphemy, murder, theft, injustice), and which the proselytes would already be following, leaves these three:
- Worshipping idols.
- Sexual immorality.
- Eating meat that has not bled to death (e.g. strangled or diseased, or still alive (oysters)).
These prohibitions correspond almost exactly to the list defined by the Council of Jerusalem.
— from my answer to Were there implicit laws not referenced in the Acts 15 letter to gentile believers?
The second and third problems were much more difficult, and many of Paul's epistles contained warnings about pushing proselytes too quickly and about being on the watch for outside influences.
(Many of these writings are taken by many today to be the exact opposite, and claimed to somehow be about Christians that were following God's laws too closely.)
The Roman Church
TLDR: Anyone that suggested keeping a kosher diet would have been branded a heretic and Judaizer, and their writings would have been destroyed.
The original Christian Church didn't naturally grow into the Roman Church during that missing period of history.
In fact, the Roman Church had existed long before Christianity.
Its leaders saw a threat from the rising popularity of this new Jewish sect, and initially tried to suppress it by force (e.g. "feeding Christians to the Lions in the Colosseum").
When this failed, they used a kind of syncretism to usurp the Christian Church.
They assigned Christian names and meanings to their existing Gods and practices, and called themselves the Christian Church.
After that, anyone that developed a curiosity about Christianity would end up with the Roman Church, and anyone that tried to follow the original Christianity was branded as a heretic and a Judaizer.
For more than a thousand years after that, whenever anyone studied the Bible, discovered its truths, and tried to revive the old religion, the entire organization was persecuted and killed.
See my answer to church history - What Pagan elements were adopted in christianity? - Christianity Stack Exchange.
And
2nd century Statue of Isis — Wikipedia:Today's featured article/May 29, 2021.
See also my answers to other similar questions from Biblical Hermeneutics Stack Exchange: