The authority of scripture is something that most churches hold to and also about having to defend it. The very nature of the Bible claims to have a universal and covenantal right to reign over all and pass said judgments and blessings. It is within this full world spectrum that people are offended (insulted) that the Bible is offensive (intrusive), in that it is on the offense (attacking) as being present in the world. Christians then form a defense that not only buttresses their personal reasons for why they hold to the authority of Scripture, but in doing so buttress why their opponents stand guilty for not adhering their beliefs and lives to Scripture. Being a covenantal document (as a whole) the Bible speaks to all the world about what God has done to provide redemption and what it is to be included in that redemption. It is then naturally offensive to say to the Jew, Muslim, Mormon, or what have you that they must conform and submit to the authority of God as found in the Bible.
Many Christians think that their defense of Scripture as to their personal authority is similarly equal to that of why others follow and believe what they want in opposition to Christianity. We think we voice our reason for belief and others their reasons for unbelief that it ends in a “your okay, I’m okay”, “we agree to disagree” stance. But it is not the same. To defend the authority of Scripture over us and why we believe it is, at the same time, to defend why it is authoritative over everyone. It is this covenantal aspect that prevents us from looking into the Bible and just seeing it as something that only speaks to us just as the Quran speaks to a Muslim. Because there is a covenant established by God that pronounces blessings and cursing we have to also believe that this is not just something that impacts me and my personal religious experience, but that it has universal implications over the whole world.
It is no surprise then why all other religions and philosophical positions avoid fighting with one another and all gang up on Christianity (We’ll never see Higher Criticism evaluate the Quran the way it has the Bible, or books trying to determine the real words of Muhammad). They do so because they collectively know that if there are Christians at all, then they stand representing a book of God’s making that holds THEM under its authority; an authority they are not willing to recognize and therefore want to fight to get out from under. In a similar fashion the language of Atheists is interesting because they see the authority of Scripture as form of tyrant. They present that the good news is to be set free form such a tyrant and venture out on our own; the modern day temptation of Adam and Eve, and error of the prodigal son rolled together.
Lastly via the authority of Scripture, Christians can state that the Canon is closed. The redemptive plan is fulfilled and the promise of the second coming established. Outside of this there is no reason to expect or need further or new revelation (as claimed by Charismatic’s, the Muslims under Muhammad, the Mormons under Joseph Smith and so forth). No new books of the Bible need to be found, written, or person revelations told. As Paul states so emphatically, anything different preached other than what is already received is to be considered cursed of God. So the Christian goes forth into the world expecting to be resisted, and yet the world does not resist them specifically but they resist the Word and authority of God. Yet there is a promise that through preaching some will hear God, repent and believe. God does currently rule and reign from heaven. The Christian does not seek to establish this, via his personal belief and defensive arguments; it is the unbeliever who instead seeks to remove this fact from their mind via manmade religious observances that are self serving. By self-serving I mean in the sense that all false religions have man at the center of what they want God to approve. For example gay rights advocates want God to be accepting of such a “lifestyle” of sin, instead of admit they are in sin and need to repent (turn) from it.