Here is what this passage is NOT about

…knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit.
2 Peter 1:20-21 

Here is what this passage is NOT about:

Some, who do not want the common people to read the Bible, cite this passage to validate their position.  The position is false and this passage isn’t talking about that.

There are some, however, who do misinterpret the Bible, which we are not free to do.  We must interpret the Bible in light of the rest of the Bible, as understood correctly by the majority of the Church.  While that is true, this passage isn’t speaking about that either.

Here is what the passage IS about:

The Bible was not written by mere men according to their own desires and purposes.  Rather, “all scripture was given by inspiration of God” (2 Timothy 3:16). God spoke through human writers, using their vocabularies and styles, in such a way that the words written are the very words of God.  That the Bible is inspired by God literally means it was “breathed out” by God—again emphasizing that the very words of scripture came from God, not men.

What difference does this make?  When we read or hear the Bible, we are reading or hearing the very words of God.  Let us receive them as such.