After all that effort in answering my questions, I only just found your post Omya, my apologies. I sometimes miss entire threads on this forum, and well, I'm sorry it's taken so long.
Where to start
I think to quote two Surah's and then ask you to correct me if my assumptions are not correct based on what these Surah's say, and what you have written in your post.
First the Surah's
Surah 3:70-71
You People of the Book. Why reject you the Signs of Allah, of which you are (yourselves) witnesses? You People of the Book! Why do you clothe truth with falsehood, and conceal the Truth, when you have knowledge.
Surah 3:78
There is among them a section who distort the The Book with their tongues. (As they read) so that you would think it is a part of the Book, but it is no part of the Book, and they say, "That is from Allah" but it is not from Allah. It is they who tell a lie against Allah, and they well know it.
Now, my thoughts for you to discuss
These two surah's seem to say two things
1. The knowledge that the People of the Book have they are concealing.
2. The Book is trustworthy, but the way it's interpreted is not.
Allah appears to be saying here that the Book is trustworthy, it's the way it is the way it's interpreted by A SECTION who distort it. Now, most Christians who honour the Bible would agree with this.
But, notice that Allah calls them the People of the Book, and honours them by telling readers of the Qur'an that they(the People of the Book) do have the revealed Book and that what is said in the Book is trustworthy, but some sections of Christendom have wrongly interpreted it.
You know, many Christians would definitely agree with Muhammed on that one.
The other thing I have mentioned earlier, but no one has discussed, is that it's important to remember that Muhammed's revelation, came at the time when the Bible was in the form as it is today and the even in the translations are substantially the same as today's Bible and is based on manuscripts that go back centuries before Muhammed. This was the same Book that the Qur'an teaches you should be reading.
In the Law of Non Contradiction it is a simple reality statement that a rose cannot NOT be a rose. Likewise, the Word of God cannot NOT be the Word of God, so all discussion on contradictions either for the Bible or the Qur'an (and there are many of those as well) are really not necessary, for that is not the issue at hand. If the Bible is the Word of God, then it IS the Word of God and cannot NOT be the Word of God.
Surah 15:9 states
We have, without doubt, sent down the Message, and We will assuradly guard it from corruption
Now compare that with what God says of His word
Isaiah 40:8 The grass withers and the flowers fall, but the Word of our God stands for ever". (the words God gave to Isaiah the prophet to proclaim to His people as a word of comfort to them)
Please tell me if you understand how it can be true. How can the Word of God be corrupted by man. Is man greater than His creator? Did the creator allow corruptions to come into His word when he promises it will stand for ever?
Now I know that you might then say that well in the Qur'an He has kept that promise, but what of his other words in the Bible which are equally His Word. He not only promises that His words will never come to an end, He promises that no part of it will pass away in Matthew 5:18
I tell you the truth, until the heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law, until everything is accomplished."
Now, you correctly pointed out that 1 John 5:7,8 are in the text, but the footnotes mention that they were not in the Greek manuscripts found before the sixteenth century. Often this is pointed out as a way of showing that the Word of God has been added to. Now, wouldn't it be far simpler for people wanting to corrupt the Word with an untruth about the Trinity to simply leave it in the text without commenting on it's origins. The Word of God is true to itself, any time any query exists, it is commented on the newer translations. Why are they not removed? Because after the finding of the Dead Sea Scrolls in 1947, which come from the last century BC and first century, other manuscripts may yet become available to add even more authenticity and clarity to the Scriptures as we know them today. Isn't it better to leave them there as all scriptures are considered the Word of God, until such time as they are proven otherwise, and if there are any doubts, isn't it more honest to document them in the text, as is the case today? God will not allow His word to change. It is His Word.