I'm wondering were are some passages in the NIV, like: Matthew 17:21 Matthew 18:11 Mark 9:44 Mark 11:26 Mark 15:28 Luke 17:36

And some more. Also there are some passages where the NIV delete some phrases as in Matthew 5:44 NIV

But I tell you, love your enemies and pray for those who persecute you

KJV

But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you

I don't understand the need of change the bible as it was for so many years, I personally find the old versions really rich in culture and those express much more than the news versions does. Also in the Old versions, the points and commas were really important to don't change the original meaning. And the Bible teaches that God is the one that gives us revelation through the Holly Spirit to understand the scriptures, so there's no need to change the Bible to make it 'more understandable'

And finally in the bible says:

Revelation 22:18-19 KJV

For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: 19And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.