I became a witness due to my older brother talking to me. Surely your brother has witnessed to you so tell him this. You were looking into things and every encyclopedia or other reference (especially see www.607v587.com, but don't tell him the source) says the date for the destruction of jerusalem is 587bce and not 607. That would mean that 1914 could not be the end of the gentile times and most importantly then 1919 could not be the date God picked the WT to be his organization on earth.
Gently ask him if he can show anyone other that Jehovah's Witnesses that point to 607 as Jerusalems fall. This could prove to be a very important moment. (FYI two of the five brothers who wrote the Aid to Bible Understanding were disfellowshipped over this issue of 587 vs. 607.)
It's like the Catholic church burning people for saying the world is round (I don't know if they really did that.
The 587 date is rock solid, as you will see as you do some reading. He will read up and tell you that witnesses use the date 539 as their touchstone date. They add two to get to 537 and then because Jerusalem was supposes to be desolate, (they say 70 years when the scriptures really say the nations around not just Jerusalem), they will subtract 70 from 537 to get to 607. They then us a scripture that talks of 7 times, which is extrapolated to be 2520 years which when added to 607 takes you to 1914.
Likely I've either bored you to tears or confused you. Sorry, but here is the point. The date 587 is a very solid historical date with over 10,000 table records pointing to it. That means that the WT is teaching 1.) a falsehood that they know about as hundreds or thousands of witnesses have left over this issue and written them in minute detail. 2). they couldn't have been picked by God in 1919.
You have to be very gentle as you talk to him as you can scare him off with "apostate" phrases. Don't tell him you have been on the internet. That is forbidden almost to them. Just go with neutal sources and ask innocent questions and let him stumble over the answers.
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Confusedjw