God's Elect are those with their IDs (names) written in the Book of Life of the Lamb before creation. It means that God knows who is who even before creation.
However the scenario is, if your mayor and only your mayor knows that you are a criminal then he puts you to jail. Then what says you? A lawful and fair realm doesn't operate this way. All you need is an open and fair judgment by an assigned judge and a group of juries. You will be judged in accordance to law instead of the knowledge of your mayor.
Similarly, earth is for such a fair and open and well-witnessed judgment, even though God knows before hand who is who.
Predestination means some of us are predestined in a way that who we are will be fully shown and displayed by the choices we make. This process can be witnessed by the angels, by the saints such as Moses (the accuser of the Jews). This process process can also be witnessed by Satan (and possibly his angels).
Revelation 12:10 (NIV2011)
Then I heard a loud voice in heaven say: “Now have come the salvation and the power and the kingdom of our God, and the authority of his Messiah. For the accuser of our brothers and sisters, who accuses them before our God day and night, has been hurled down.