I am going to assume that since you asked the question to Christians that an aceptable answer will be rooted in our worldview. For reasons that I will lay out we have to look to the Bible for what it says about itself. While this may appear to be circular, and I guess in one regard it is, we are claiming that ultimately the Bible is the authoritative revelation of God's truth and character. In the Christian worldview there is no other place to start.
Your question of use is a great one. Practically the Bible has one purpose, to tell the story of the fall of man, the inability for us to live up to God's standard, His plan of salvation for us through His Son, and the final restoration and redemption of this world. Within that though we have commands from God in the OT, Christ and the Apostles (Law), poetry and proverbs that give us wisdom and show us how to worship, and instruction on how to live out our faith in practice. So I guess the answer is "All of the above". For specific reasons why the Bible is the source for all of this, read on.
The Bible is the foundational theological text for Christians for 4 reasons:
- The Bible is the inerrant authoritative Word of God
- The Bible is clear
- The Bible is necessary for the Christian faith
- The Bible is sufficient for the Christian faith
With these 4 reasons in mind Christians look to the Bible as the revealed Word of God that tells His great story of redemption for this world, shows us how to seek Him for ourselves and trust Him for our eternal lives. Academic study aside, this is the point of Christian theology, to know and love God.
I’ll offer brief summaries of these points and point to sites or books on the topic if you want deeper insight
The Bible is the Inerrant Authoritative Word of God
First off the Bible claims clearly to be the direct Word of God. In the Old Testament verses like Jeremiah 1:9 show this explicitly how God spoke to His prophets:
“Then the Lord put out his hand and touched my mouth. And the Lord
said to me,”
Additionally the Bible states that God “spoke through” the prophets, who words and teachings are the primary source for the Old Testament:
“But neither he nor his servants nor the people of the land listened
to the words of the Lord that he spoke through Jeremiah the prophet.”
Next, in the New Testament in Timothy we see the endorsement of the whole Old Testament as the direct Word of God.
“All Scripture is breathed out by God and profitable for teaching, for
reproof, for correction, and for training in righteousness, 17 that
the man of God may be competent, equipped for every good work.”
2 Timothy 3:16
The word for scripture here in the original Greek is graphe. In every occurrence of this word in the New Testament (51 of them) this word is used to refer directly to the OT. Also, note the phrase, “breathed out by God”. This is a claim that all of the scriptures come direct from God.
Finally in the New Testament we also have internal attestation to it’s nature as the Word of God.
“our beloved brother Paul also wrote to you according to the wisdom
given him, 16 as he does in all his letters when he speaks in them of
these matters. There are some things in them that are hard to
understand, which the ignorant and unstable twist to their own
destruction, as they do the other Scriptures.”
1 Peter 3:15-16
The key thing to note here is that Peter uses the same Greek word we talked about above when he says “other scriptures”. Peter here directly places the letters of Paul alongside the Old Testament as graphe, or scripture.
Furthermore, the Bible is inerrant. But what does this really mean? Quoting Wayne Grudem, “The inerrancy of Scripture means that Scripture in the original manuscripts does not affirm anything that is contrary to fact.”
Just one note on a very plain explanation. Note the insistence upon the original documents being inerrant. My ESV translation is not inerrant, your KJV is not inerrant and the RSV is not inerrant. The Bible is fully true in the original documents.
The following Biblical claims to it’s own truthfulness build upon the statement that scripture is the direct word of God. The Bible is pure:
“The words of the Lord are pure words, like silver refined in a
furnace on the ground, purified seven times.”
The Bible is perfect:
“I have seen a limit to all perfection, but your commandment is
The Bible is true:
“Every word of God proves true; he is a shield to those who take
refuge in him.”
The Bible is Clear
This may seem odd given the amount of confusion and discussion that goes on, but the Bible claims to be clear and that every man can understand what the Bible says about God. The whole nation of Israel was expected to know and understand the scriptures. As Moses instructed the people:
“And these words that I command you today shall be on your heart.
7 You shall teach them diligently to your children, and shall talk of
them when you sit in your house, and when you walk by the way, and
when you lie down, and when you rise.”
David states that Word of God makes things understandable to us:
“The unfolding of your words gives light; it imparts understanding to
If this is true, why do people misinterpret or disagree on what the Bible says? It is because of our own shortcomings. If the Bible is inerrant and the revealed Word of God then it is our standard, not our own understanding. This is a tough teaching to take, but we are instructed to approach God and His Word humbly, and that is certainly a counter-cultural idea these days.
The Bible is Necessary
The Bible is necessary for our faith; we cannot know God apart from the Bible. As Paul says:
“For ‘everyone who calls on the name of the Lord will be saved.’
14 How then will they call on him in whom they have not believed? And
how are they to believe in him of whom they have never heard? And how
are they to hear without someone preaching? 15 And how are they to
preach unless they are sent? ... 17 So faith comes from hearing, and
hearing through the word of Christ.”
Romans 10:13-15 & 17
Paul nailed this one on the head, so I will leave it there.
The Bible is Sufficient
This point is disputed often in its meaning, so I will do my best to be clear. When we says the Bible is sufficient we are saying that God has given us everything we needed to know for our salvation, for trusting Him perfectly, and for obeying Him perfectly. We do not need anything outside of the Bible to know who He is.
As this could be a whole topic on its own I will just cover a few references to back this up. Paul tells Timothy that, “from childhood you have been acquainted with the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus” in 2 Timothy 3:15. Additionally in verses 16 & 17 Paul goes on to state that the scripture is “profitable for teaching, for reproof, for correction, and for training in righteousness, 17 that the man of God may be competent, equipped for every good work.”
This is an affirmation that the scripture contains the knowledge we need for salvation, and to be fully equipped for the good works that Christ called us to.
As a closing note, I will state that I think you will get a small, but varying, group of different answers. Different Christian school of thought view the Bible in slightly different ways. I do not think there is universal consensus in the broader Christian church on this question when you get down to the details, so I would expect to see that reflected in the answers here.
My main source for this summary is Wayne Grudem’s excellent book, Bible Doctrine. I highly recommend it for an even further study on the subject.