JW's, Mormons, Armstrongs, Baha's -- nice people yet deceived, page-44

"Here is a reference I have read. Nowhere have I read that the authenticity of the text from Matt 28:18-20 has been challenged. Why would it be?"

That's interesting and as mentioned a little surprising.
Perhaps it's challenged because it does not correspond with other NT baptismal formulae and because it is an example of how NT writings were adjusted in the course of their journey of inclusion in the "official" Bible.

Whilst it's true that ...
“This text, however, taken by itself, would not prove decisively either the personality of the three subjects mentioned, or their equality or divinity.”
it's also true that Matthew 28:19 is used as support and proof of the Trinity doctrine. Even on HC.

Here are a couple of the many sites that have assembled various references as to it's authenticity.
https://www.jesuswordsonly.com/topicindex/633-matthew-28-19-in-original-gospel-of-matthew.html
http://www.trinitytruth.org/matthew28_19addedtext.html

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