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Every doctrine that is unique to Jehovah's Witnesses is in fact extra-biblical.
Here are a number of examples
1. that their leaders somehow represent the Faithful and Wise Servant
2. that the book of Revelation is about them
3. that Jesus presence (parousia) began in 1914
4. that Jerusalem was destroyed in 607 BCE
5. that there are two classes of Christians (anointed and non-anointed)
6. that only faithful Jehovah Witnesses have a scriptural hope of surviving Armageddon.
7. that the name Jehovah is in the New Testament
8. that making God's name known involves telling people God's name is Jehovah.
9. that whole blood transfusions are outlawed in scripture.
10. that something scripturally significant happened in 1914, 1918, 1919, 1925 or 1975
11. that the tribulation spoken about in Matthew 24 is future
12. that WTS leaders can interpret Bible prophecy
13. that less than 150,000 faithful Christians existed prior to the 20th century
14. that only 144,000 people have a heavenly calling.
15. that 8 men in New York have been given the exclusive mandate and ability to interpret scripture.
16. that only Jehovah's Witnesses are real Christians
17. that "this generation" in Matthew 24:34 does not mean the generation Jesus was manifest in
18. that the 1914 generation is still with us