All scripture is God-breathed and useful for teaching, rebuking, correction, and training in righteousness.
-- 2 Timothy 3:16
The first thing 2 Timothy tells us about Scripture is why it is useful -- because Scripture comes from God.
Old translations of the verse use the word inspired, reading "All scripture is inspired by God."
The Latin Vulgate translated the Greek as divinitus inspirata, and inspirita passed into English as "inspired" through the translation of Wycliffe.
The interesting thing about the Greek word is that, strictly speaking, it does not refer to inspiration at all.
That is not to say that inspiration is not a valid theological term. It is.
When we think of inspiration we think of the power of God guiding the writers of the Bible so that what they wrote, even though they wrote in their own language and with their own vocabulary and on the basis of their own experience, was nevertheless exactly what God wanted written.
The word inspiration refers to this. Inspiration means "breathed into," from in meaning "in" or "into" and spiro meaning "breathe." It describes the process of God's revelation of Himself in Scripture from a human point of view. However, this is not the meaning behind the underlying Greek word in 2 Timothy 3:16.
Theopneustos, the Greek word used, combines the word for "God" (theos) and the word for "breath" or "spirit" (pneustos). It means "God-breathed," and
is the translation used by the New International Version.
It teaches that Scripture is the result of this breathing out of God. Much as God created man by breathing into him and making him "a living soul," God also breathed out the Scriptures so they became a living revelation.
Paul is not talking about how human authors of Scriptures received God's revelation. He is talking about Scripture itself, saying that the words of Scripture are the words of God, and this is what makes Scripture so useful.
A book containing merely human words might be true and useful to a point.
An instruction manual for your new dishwasher helps you run the appliance. The operator's book on your new car is useful.
If you want to learn Latin, a book teaching you Latin will be useful.
But there is no comparison between human books, useful in limited ways, and the Word of God useful in the ways Paul spells out in 2 Timothy 3:16.
-- James Montgomery Boice, Standing on the Rock,
Chapter 6, The Most Useful Thing in the World
The LORD God formed the man from the dust of the ground
and breathed into his nostrils the breath of life,
and the man became a living being....
Genesis 2:7