“All scripture is inspired by God and is useful for teaching, for reproof, for correction, and for training in righteousness.”
The “Scripture” being referred to would be the books of the Old Testament. The passage probably does not refer to the Old Testament as a completed collection (a “canon”), since the canonization of the Old Testament was not yet firm for Christians by the end of the first century C.E., although it might well have been for Jews. Nevertheless, the passage shows that an authoritative scriptural tradition was well underway by the time that 2 The companion on Paul's later journeys for whom two pastoral epistles are named... More was written. The false teachers of the era may not have regarded the Old Testament books as authoritative. What the author means by “inspiration” is contested. The emphasis of the passage is not so much on inspiration itself, but upon the use of Scripture, that is, its functions for guidance and instruction.