The very, very short answer is that the Protestant Reformation was deeply concerned with the original, unfiltered meaning of the Biblical texts. While sola fideles, faith alone (rather than works) leading to salvation, is perhaps the famous of the Reformation’s slogans, sola scriptura, Biblical text alone, was another. They wanted to recreate, really to rediscover, the original Biblical commadments, unfettered by Church doctrine.
To do this (in Western Europe), of course, meant putting the texts out of Latin into the vernacular. Myriad translations predate the Reformation. Wycliffe's Bible is perhaps the most famous pre-Reformation translation. But translation in the Reformation took on new significance.
The Reformation translators were standing on the shoulders of giants. Most importantly, one of the movements which laid some of the intellectual groundwork for the Reformation was the Humanist movement, which was very concerned with what today we call “lower criticism” and comparing the various versions of Biblical text in their original languages (the greatest Humanist, Erasmus of Rotterdam, despite many pleas from Reformers, never left the Catholic Church).
When the Reformers picked up the Humanists’ work and set about translating new, vernacular (rather than Vulgate Latin) versions of the Bible, they found many Hebrew Bible (“Old Testament”) books either lacked Hebrew originals or weren’t in use in among the Jews. These books were, I believe, without exception found in the pre-Christian Greek translation of the Hebrew Bible known as the Septuagint, but they are not included in the Masoretic text that Jews use today.
I believe Luther was the first to call them “Apocrypha” and said they “are books which are not considered equal to the Holy Scriptures, but are useful and good to read.” I believe they were included in Luther’s original German translation, in a separate section, and only Calvinist and Radical Reformation Bibles eliminated the, entirely.
Essentially, these are books in the pre-Christian Septuagint translation but not in the Masoretic Text used by Jewish communities in Luther’s time (and today). This discrepancy was known in the Middle Ages but, as far as I know, Luther was the first to move the Apocrypha to its own section, though he didn’t delete it entirely. It was only much later that Bibles were printed without Apocrypha, at least in English (I’m less sure of other languages). The lack of clear Hebrew original made the texts seem of dubious authorship (I believe, thought I’d have to look up further, that Medieval Hebrew versions of some of these texts today are known from places like the Cairo Geniza—version of Ben Sira or the Wisdom of Sirach, for examples, were definitely found there indicating pious Jewish use for the text even as it wasn’t being included in the formal canon).
Can you list the other 12 books please? As far as I know Protestantism only removed 7 (plus some chapters from Daniel and Esther). Unless you are including books the Orthodox consider canonical but not Catholics.
There's a lot here... First, you have to ask, which Bible and what is "the Protestant Bible"? There were notable translations into German, French, English, and other languages in the early years of the Reformation. But for the purpose of this question, I don't think it's that relevant, because as far as I know the initial 16th century vernacular translations all included the apocryphal/deuterocanonical books. I'll use Luther's translation as the prime example, though.
The next point is, it may be more accurate to say "why did Catholics definitively include those books" than to ask why Protestants removed them, because the status of those books was rather confused and disputed throughout the Medieval period. Canon lists from the early church are quite divided on these books as well; there was some evidence in their favor but never universal acceptance. From the Catholic Encyclopedia, which sums it up well:
In the Latin Church, all through the Middle Ages we find evidence of hesitation about the character of the deuterocanonicals. There is a current friendly to them, another one distinctly unfavourable to their authority and sacredness, while wavering between the two are a number of writers whose veneration for these books is tempered by some perplexity as to their exact standing, and among those we note St. Thomas Aquinas. Few are found to unequivocally acknowledge their canonicity.
The earliest unequivocal mention (that I can think of) of the apocrypha/deuterocanon as canonical by the Western (Catholic) church does not occur until the mid-15th century Council of Florence, and was reiterated at Trent in the Counter-Reformation of the late 16th century. So it's not as if these books were universally seen as canonical for a thousand years until suddenly the Reformers decided to do something different.
Anyway, when he translated the Bible into German, Luther did one thing that reflected the Renaissance humanism of the day: he insisted on learning Hebrew and translating the Old Testament from that, rather than relying on the Latin Vulgate or Greek Septuagint. The Renaissance and the Reformation both prioritized going ad fontes, returning to the original sources instead of relying on accumulated tradition. This is important for the apocryphal books, because they are later compositions than the rest of the Old Testament; there were no Hebrew texts to go back to, only the Greek. That was one strike against their canonicity for Luther, which incidentally followed the opinion of Jerome, the original translator of the Vulgate.
Nevertheless, Luther did not remove the books altogether, nor did the English-language Geneva and King James Bibles. Luther called them "good and profitable for Christians to read, but not equal to Scripture," and he translated them alongside the Old and New Testaments, though he did move them to a separate section. He also continued to quote them and read them, though I'm not sure if he preached on them or not.
The removal of certain books from the Protestant Bible, known to Protestants as the Apocrypha and to Catholics as the Deutero-Canonical books, has a lot to do with translation and a little bit to do with publication costs.
The seven books that distinguish the Protestant OT from the Catholic OT are Judith, Tobit, 1 Maccabees, 2 Maccabees, Wisdom of Solomon, Baruch, Sirach, as well as longer versions of Daniel and Esther. What distinguishes these writings from other books of the OT is that they were originally written in Greek well the rest was written in Hebrew.
In the fourth century, when Jerome was commissioned to make a translation of the Bible into Latin to replace the Vetus Latina, the various other Latin translations of the Bible, Jerome included introductions that noted some books were written in Greek only, not Hebrew. This was significant because often early Christians had worked from the Septuagint edition of the Old Testament and so paid no attention to what was written in Hebrew originally as opposed to Greek. After Jerome's edition was published, many medieval theologians expressed doubt about the canonicity of these books.
Fast forward in time to the 16th century and the Protestant Reformation. Luther desires for everyone to be able to read the Bible, so he begins to translate the text into German. He also emphasizes the doctrine of "sola scriptura" (by scripture alone). This leads him to consider the question of what is Scripture? Luther noticed that the Jews in Germany had adopted only the books that were originally written in Hebrew into their canon. (This happened for reasons that I am not totally familiar with.) This observation combined with Jerome's introductions caused Luther to argue that these books were not to be considered part of the inspired Bible. However, Luther did translate these books and included them in his edition of the Bible as a separate section. Other Protestant groups followed Luther's lead. It was not until a few hundred years later that printed editions of Protestant Bibles stopped including this third section of the Bible, mostly as a way of saving on printing costs.
They weren't originally and they stayed in the bible quite late. Here's a picture of Mary Jones' bible from the early 19th century where's she has signed her bible -but if you look at the page she's written on, you'll note (if your Welsh is good!) that this is actually from Maccabees.
Luther is normally nominated for complaining about canonical issues, as he didn't particularly like Esther, II Maccabees, James, and Revelation (Maccabees wasn't so much as a problem because it was Old Testament and therefore not so important, and he wasn't that bothered about Sirach being included either), but at no point did he not include the books. The Apocrypha was included in virtually all editions of the bible (even going back as far as Wycliffe) because there was little to no canonical discussion about them: the only possible exception might be Esdras III/IV because they're not found in the Septuagint versions, and Maccabees III/IV because they're not in the Vulgate and this leads us to the next bit - where do you get your canon from?
You've got two main options, either a Greek one (commonly called the Septuagint) or the Masoretic texts. The 4th century translation by Jerome called the Vulgate includes all the books mentioned above, and the Reformers (and their bible translators) tend to follow the books included in the Vulgate, although they might play around with the order a little. Some translators would add in different bits that others might exclude, for example Leo Juda included the books that Luther omitted, and also got rid of the Song of the Three Children, the Prayer of Manasses, and the Prayer of Azaria.
This isn't to say that Protestants all accepted the books - Calvin didn't classify them as canonical, so even though he quotes Baruch, he doesn't classify anything above the normal 66 books as canonical - plus, those deuterocanonical books/Apocrypha tended to support Catholic doctrines such as purgatory which Protestants did not accept. The Westminster Confession (1646) only accepts the normal 66 books as the others are not divinely inspired but the bibles used by the Anglican church still contained them. So while they might be printed in the bibles, they don't get used by Protestants.
Actual removal from the printing of the bibles come much later on in the 19th century, and then unevenly as other editions continued to publish them. Things come to a head with the Apocrypha controversy in the British and Foreign Bible Society (BFBS) in the 1820s which had been printing bibles for circulation on the continent with the Apocrypha included as Lutherans and Catholics still used the Apocrypha (although for separate reasons). The British dissenters and Scottish Presbyterians argued (with a long heritage I might add), that the books were not inspired, and shouldn't be printed or circulated with their money. This push was led by Robert Haldane, who had contributed £70,000 of his own money on religious activities in Scotland - a massive amount - and he, his brother, and an Irish clergyman called William Thorpe began to agitate towards removing the Apocrypha. The BFBS was actually quite liberal in attitude, and was quite happy catering to those who needed the Apocrypha. In 1826 however, the BFBS conceded the point that none of their funds were going to be used to print Apocrypha anywhere. From then on, British bibles tended to drop the Apocrypha while their Protestant Continental brethren still included them.
And where can I read them?
