It’s not true that the Bible does not say "the Bible alone. Catholics have almost gloated over this apologetics approach, thinking it to be quite secure, and succesfully tripping up many Protestants.
Trying to prove that the Bible doesn’t say a certain, exact wording, does not prove that that something is not in scripture. It could still be in scripture; in slightly different words, yet still meaning the same thing. The Bible is clear that we are not to add anything to it, and this means “Bible alone” for the Christian.
Yes it is true that the Bible does not say “the Bible alone” in whatever shape or form.
And neither is it in Scripture in slightly different words.
So let me address the verses you cited:
Add thou not unto his words, lest he reprove thee, and thou be found a liar.
The question here is what constitutes “his words”? Who determines what “his words” are. Could we say that the Catholic Church added to “his words” by declaring canonical books of the New Testament?
So here the question boils down to authority. Who has the auhority to determine what is and is not God’s word. Until you sort that one out you cannot say whether you are adding to His word or not.
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:
First question – add unto what things? Add unto the prophecies of Rev? But that is not quite the same as adding to the word of God is it? If you read it in that way, then we must eschew all other books of the Bible because the verse speaks specifically of the book of Revelation and not of the Bible since the Bible was not even compiled yet when the Revelation was written.
Therefore all other books of the Bible are additions if you interpret that verse in the way you are doing.
Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the LORD your God which I command you.
Again, if you are to take that literally, the Bible should finish at Deuteronomy. It should be limited to the Torah or books that were written prior to Deuteronomy
Now I know that Roman Catholic teachings do say that “Tradition” supposedly establishes scripture; yet the Bible warns about “tradition” of the very wrong kind.
But he answered and said unto them, Why do ye also transgress the commandment of God by your tradition?
But what tradition was Matthew talking about in this verse? Was it not the tradition of the elders e.g. washing their hands, etc. But are not these traditions prescribed exactly in the Torah, of which the book of Deuteronomy which you cited above is one?
So now, your last proof text negates the second to the last proof text.
Where does that leave you then?
Protestants teach, on the other hand, that Catholics have added the Apocrypha, while enduring Catholic counter-claims that we “removed” the Apocrypha from the Bible.
“Bible Christians” are just that. They base their teachings on the Bible alone.
Bible Christians are therefore most definitely not “just that”. With their belief comes a doctrine, a doctrine that is not found even in the Bible.
Furthermore, Bible Christians give tacit approval to the infallibility of the Catholic Church by accepting the Bible.
And yes, the protestants removed the books of Deuterocanonicals from the Bible. History proves that.