prophecy never had its origin in the human will, but spoke from God along by the Holy Spirit

2 Peter 1:12-21
So I will always remind you of these things, even though you know them and are firmly established in the truth you now have. 
For we did not follow cleverly devised stories when we told you about the coming of our Lord Jesus Christ in power, but we were eyewitnesses of his majesty.
Above all, you must understand that no prophecy of Scripture came about by the prophet’s own interpretation of things. For prophecy never had its origin in the human will, but prophets, though human, spoke from God as they were carried along by the Holy Spirit.
God's purpose for his people is that they should come to share his own nature and character - nothing less. So to faith must be added other qualities. In this way knowledge of Christ is translated into action. Peter does not hesitate to refresh his readers' memory of truth already known, especially as he sees his own death approaching.
Why?
Peter likes to remind followers that what he established are in the truth and he is the witness of Jesus is the son of God.
There will be many prophecies of Scripture, but do not trust in them, for real prophets are came from the Lord and they were carried along by the Holy Spirit.
How?
We believe that Jesus Christ is the son of God and obey the leading of the Holy Spirit and God's word.