Why do Bible versions differ‪?‬

I have been wondering for quite a while why Bible versions differ? Especially since we know that our God NEVER changes. So if He never changes, surely His word must also always stay the same?

In this book the Authorized King James Version Holy Bible (KJV) is compared with the New International Version (NIV) and other modern translations to enable the reader to decide for him/herself whether the message in the modern "Bibles" are still the same or not. And if not, why not?

It is all about the Received Text which has always been used in Bible translation, versus some corrupt manuscripts which are used by the enemy to let God's children doubt His Word.