@sjw at least as far as the matt 17:21 thing goes, it would appear that the original transcriptions may have been incorrect and taken parts from other manuscripts. i don't know if that's true but ultimately it doesn't matter much because there is probably a shit ton of stuff in the bible and out of it that has been changed and altered over the years that we don't know about and never will know about.

the best thing to do is to read, pray, and work from there.