When used in the New Testament, “Scripture” translates a word based on the Greek “graphein”, “to write”. Different translations into English might say “the Scriptures”, “Scripture has it”, “it is written” or “the writings”. I’ve never actually seen the last, but I personally think that that usage is how it would have struck a first century AD reader. Almost always these referred to a set of Hebrew holy books that had been translated into Greek in Alexandria around the third century BC, with some books considered holy that were available originally only in Greek.
After the destruction of Jerusalem, a school of rabbis set up shop in Jamnia and around AD 90 to 110 settled on the determination that they would consider as the Jewish inspired writings only those books of the Torah and Tanakh that were originally written in Hebrew, and the Septuagint specifically was not inspired. This is because the Septuagint was very explicit in some prophecies that were more subject to interpretation in the Hebrew. A prime example is Isaiah 7, where “a virgin shall be with child” uses a compound word in Hebrew - young woman, with the usual meaning of “virgin” (like German “Jungfrau”) - whereas the Septuagint uses a specific Greek word that only means “virgin”. Also, the removal of the books of the Maccabees was satisfying to the Roman occupiers, who wanted no more holy references to Jewish uprisings. This determination of the Jewish scriptures prevails in much of Judaism to this day.
Christians continued to consider the Septuagint as inspired for the Old Testament, plus some writings of the apostles and first century evangelists which we now know as the New Testament. The mix of letters considered inspired for the New Testament varied somewhat in different places, and was fixed in 397 for the Christians of North Africa by a synod of bishops who published a definitive listing those books considered inspired in both the Old and New Testaments. St. Augustine in his On Christian Doctrine provides this listing, which we all recognize today as the Catholic Bible. It as much codifed prevailing practice as defined it, and throughout Rome and Western Christendom for the next 1100 years became accepted as the defined canon of Scripture.
Martin Luther, who resented the Maccabees’ insistence on prayers for the dead and implication of purgatory, and Tobias’ insistence on alms and good works, decided he would accept as definitive the judgement of the “council of Jamnia” mentioned above with regard to the Old Testament, even though there were no Christians present and the decision was motivated in large part by a desire to undermine the preaching of the Gospel. Accordingly, the ecumenical council of Trent defined the canon of Scripture formally. The books rejected by the reformers are those they call “apocrypha”. Luther wanted to reject Hebrews and James as well, but could not resist popular opinion.
It is worth noting, then, that the Bible (however defined) was considered inspired by God and its authority unquestioned because of common unquestioned usage over 1500 years. Its authority, mentioned above, is based on its authorship by God. We only know this, though, because it is part of God’s revelation preached by the Church (however defined).
It is worth noting, as well, that the phrase “the word of God”, when used in the New Testament not with reference to Jesus Christ, refers to “the gospel message” and not to the Scriptures per se. This is not to say that the Scriptures are not properly called “the word of God,” only that the New Testament doesn’t use it that way. In Acts 17, the Bereans “were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so.” Obviously, they didn’t search the scriptures to find out if the scriptures were so. Apart from which, nobody really believes that St. Paul and the others went around handing out Bibles.
