They are united (all believe the same thing, do the same thing, say the same thing -religiously speaking)
WT brags about this point, but really, what choice does a JW have? A JW must believe everything the GB teaches without question and regardless of evidence to the contrary; dissent is dealt with swiftly and harshly. Rather than being a bragging point, it's actually one of the most embarrassing things about JWs- 7 million+ minds that have been switched off.
Christ's presence started invisibly in 1914.
Except that it was originally pronounced by WT to have happened in 1874 and preached thusly for almost 60 years. Except for that, yes, Jesus' presence began in 1914.
JWs are to be no part of the world.
Except for the whole UN/NGO thingy, Rutherford's sedition against the US Govt, his attempted alliance with Hitler, etc, etc. Other than these, and more, examples of blatantly currying favor with the world, yes, WT is "no part of the world".
Preaching house to house is a must for all christians that are able to.
Despite the fact that not one scripture says Christians preached from door-to-door, no commandment saying as much exists, and no record exists that Jesus ever did it.
Other than that, yes, it's a requirement for Christians.
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WT doesn't so much have "core" doctrines as it does doctrines du jour.