RE: What a ridiculous argument. The only Bible in existence at that time was the Hebrew Bible
I don’t see how the author’s statement is ridiculous. The Bereans compared Paul’s teachings to the Old Testament teachings about the coming Messiah.
In other words, the Bereans USED the scriptures available to them then to evaluate what Paul taught and for that, they were commended.
Of course, and to be extra-Biblical means that what is taught was not predicated on what preceded it and was promised and in confirmatory conflative fulfillment or expansion of it, such as the promised Christ (Mic. 5:2) being the suffering atoning scapegoat (Lv. 16, Is. 53) so that men and Peter preached, "To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins" (Acts 10:43) by which the promised New Covenant (Jer. 31:31-33) began, and thus thousands of devout Jews and then Truth seeking Gentiles believed. Glory to God.
For an authoritative body of wholly God-inspired writings had been manifestly established by the time of Christ as being "Scripture, ("in all the Scriptures") "even the tripartite canon of the Law, the Prophets and The Writings, by which the Lord Jesus established His messiahship and ministry and opened the minds of the disciples to, who did the same . (Luke 24:27.44,45; Acts 17:2; 18:28, etc.) And the Hebrew Scriptures testify to Jesus being the promised scapegoat and perfect atonement, and thus Scripture provided the **doctrinal and prophetic epistemological foundation for the NT church.
Which established its Truth claims upon Scriptural substantiation in word and in power, in dissent from the magisterial stewards of Scripture, with even the veracity of apostolic preaching being subject to examination by Scripture.
For God manifestly made writing His most-reliable means of authoritative preservation. (Exodus 17:14; 34:1,27; Deuteronomy 10:4; 17:18; 27:3,8; 31:24; Joshua 1:8; 2 Chronicles 34:15, 18-19, 30-31; Psalm 19:7-11; 119; Isaiah 30:8; Jeremiah 30:2; Matthew 4:5-7; 22:29; Luke 24:44, 45; John 5:46, 47; John 20:31; Acts 17:2, 11; 18:28; Revelation 1:1; 20:12, 15 And thus as abundantly evidenced , as written, Scripture became the transcendent supreme standard for obedience and testing and establishing truth claims as the wholly Divinely inspired and assured, Word of God. Thus the veracity of even apostolic oral preaching could be subject to testing by Scripture, (Acts 17:11)
In addition that God could inspire men to write His word and provide new public revelation thereby (in conflation with what had been written) has its precedent in the Hebrew Scriptures.