The belief in predestination is such a wonderful topic to study in the Bible! Christian denominations have been built, or broken, on misunderstanding this doctrine. John Calvin, one of the founders of modern-day Calvinism, is arguably the most well known proponent of predestination (although it was first formulated by Augustine).
One popular dictionary states that predestination teaches that the final salvation of some people is ordained from eternity by God (Collins English Dictionary). Calvinism itself defines this teaching as the "eternal decree" of a perfect God who has, based on his will, already foreordained the eternal destiny (i.e. heaven or hell) of each human being before they are even born. We need, however, to rethink the ramifications of this belief.
You could be the saintliest person on earth, yet despite all your goodness, you could end up in eternal torment due to this erroneous teaching. Another person, on the other hand, could be the worst sinner on earth, yet because God foreordained him he could spend eternity in paradise. We may as well live a life of hedonism because it will not make one bit of difference in the end if this false teaching is true.
Justification
The primary Bible verse used to justify predestination is in the Apostle Paul's epistle to the Romans, chapter 8. This verse states the following.
Because those whom He did foreknow, He also predestinated to be conformed to the image of His own Son . . . (Romans 8:29, HBFV throughout).
What does this controversial verse on predestination, in Romans 8, mean? David Brollier explains this concept as follows.
"He (God) knew our sinful nature would preclude that (conforming to Christ's image), so he extended his grace to all who would accept the sacrifice of his son for our sins. His goal was that we would be exactly like his son in holiness and purity, but knew that without his power reigning in us it could never happen."
Note that predestination does not just affect certain people but all mankind. What Paul is teaching does not concern salvation per se, but God's desire that we be conformed to his son, Jesus Christ. The book of Ephesians tells us he planned, from the moment he determined to create the earth, that man would populate it, and no other beings but mankind should become his children (Ephesians 1:3 - 4).
We are also told in the Bible that it was foreordained (a type of predestination in the sense that the Eternal decided in advance what he, not we, will do) that those who believe and obey the eternal God should be adopted by Jesus himself, through whom we have an inheritance according to his will (Ephesians 1:11).
Conclusion
The Bible's definition of predestination has nothing to do with whether a person will or will not receive salvation no matter what they do. Our Father's ultimate decision regarding our eternal fate rests on what we choose, or not choose, to do. As John Didymus Pope said, if God already has determined, in advance, just one person to die forever we would have to get rid of John 3:16.