What does 2 Peter 1:21 mean?
In the previous verses, Peter pointed to his personal witness of the transfiguration of Jesus (2 Peter 1:16–18). For him, this was an absolute confirmation of the prophecies of Scripture which pointed to the Messiah. As a result, Peter not only believed in Christ, but he was assured of the other prophecies, which speak of Jesus' return as judge and king.Here, he repeats his statement from the previous verse: These prophecies were not invented by human minds. They were not "cleverly devised" stories (2 Peter 1:16) meant to deceive, and they were not insightful human predictions meant to encourage. Rather, these prophecies came straight from the mind of God. The prophets spoke God's Words as they were carried along (or "moved") by the Holy Spirit. This is proven, in part, by the fact that they are confirmed. And, more powerfully, by the fact that they are not simply guesses or speculation. These are specific prophecies, which were specifically fulfilled.
In other words, the prophecies of Scripture are the words of God about the actions of God. And God always accomplishes what He sets out to do.