Some points to keep in mind....
1. There has NEVER been an ecumenical council or decision on this - ever.
2. Several individual denominations have - in some formal and official manner - at least determined what IS Scripture (but rarely ruling on what is NOT), but this has ONLY been for that specific denomination. I know the RCC did this (at Trent in the 16th Century), the Anglican Church did so (also in the 16th Century). I don't think the Orthodox Church has, I know the Lutheran Church has not. I can't speak for any of the others....
3. God tends to work through His people. The consensus around 66 books was and STILL IS absolutely stunning and remarkable! Now, yes - about 7 of the NT books were of lesser standing or somewhat debated (Revelation STILL seems to have some issues among some) - but that debate calmed to a whisper by the end of the 4th Century. Yes - there are some still debated books that LACK consensus related to before Christ (although possibly written after Him); there is no consensus here: The OO has one set (well, several - it doens't even agree with itself on this), the EO another, the RC another. Those that embrace these can't seem to agree with ANY but SELF exclusively on this (and often, not even self). So, we have 66 with a stunning, absolutely stunning, common and historic consensus (and have for a very, very, very long time). A few extra DEUTERO books are floating around - with no consensus beyond 4 denominations or so, and not among them.
4. I realize, a FEW Orthodox and Catholics seem to be VERY concerned, even deeply troubled in their soul, over the reality that not a single one on the planet agrees with their denomination on what is and is not Scripture. I understand and sympathize. But the grief they feel over this is simply not necessary. These books are incredibly moot - the reality is, no one really cares - one way or the other. Lutherans including the unique Catholic set in our tomes (EVEN BEFORE the RCC chose them, officially!) well into the 20th century. So what? There's just nothing in them of any doctrinal consquence. Have you read Psalm 151? Do we REALLY need to FIGHT over it? Don't we have MUCH bigger fish in the sea? READ IT! Hey, if our Greek Orthodox friends want to include in in their tomes and read from it in their Sunday lectionary - I'm 100% fine with that. But, PERSONALLY, I'd rather focus on the 66 the whole church has always embraced - where no debate and controversy exists. But again, if my Greek friend wants to embrace Psalm 151 as Scripture: God bless him. It reminds me of the ABSURD fight over "...and the Son" in the Creed. Okay - may not be ecumenical but it's just not an issue. Buy an KJV with the RCC's unique books it - or a Lutheran one with those, or get yourself a new English Standard Bible but out by some Protestant publisher without them. Doesn't make a bit of difference (I know - unlike nearly every Catholic known to me, I've actually READ them - word for word).
I'm moving on There are about 10,000 threads at CF of much greater importance and consequence.
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