Seems to me that free will and predetermined destiny is just a big contradiction. Can you convince me it is not?
Play chess against a grand-master of the game. Even before you begin, I could state in advance that you will lose with great certainty. Though each move you make is completely of your own free will, the ultimate outcome is known. Therefore, free will and predetermined destiny can co-exist.
The problem is not that an outcome might be known in advance, but that you are assuming that each step leading to that outcome has been just as predetermined as the final result. A person can make choices of his own free will, but the end result of those choices can still both lead to a similar result.
Mordecai said this to Esther. She had a choice of intervening to prevent the slaughter of the Jews. "And Mordecai told them to answer Esther: "Do not think in your heart that you will escape in the king's palace any more than all the other Jews. For if you remain completely silent at this time, relief and deliverance will arise for the Jews from another place, but you and your father's house will perish. Yet who knows whether you have come to the kingdom for such a time as this?"" (Esther 4:13-14). Mordecai acknowledges that the choice to intervene or not was completely up to Esther. Yet, he confidently asserted that the outcome, the rescue of the Jews, would remain the same no matter how Esther chose. Her choice would make a difference in her own life, but not in the overall plan of God.
When Paul talks about God's foreknowledge and predetermination, people jump to the conclusion that every single event of every single person has already been meticulously planned out. But few want to follow this line of thinking to its logical end. This would mean that God planned out the mass-murder of children that has happened in our world, along with all the other evils. But that conclusion would lead to a contradiction: "Let no one say when he is tempted, "I am tempted by God"; for God cannot be tempted by evil, nor does He Himself tempt anyone" (James 1:13). James goes on to point out that temptation comes from our personal desires leading us astray.
What needs to be seen is that Paul states that the plan, which gives Christians the opportunity to be saved, was foreknown by God and predetermined to be followed. God knew in advance, before the foundation of the world, that men would sin and that they would be unable to save themselves from that sin. Thus, God made a plan, before creating the world, to send His Son into the world to die for mankind's sin. In advance, He determined what needed to be done by men and the kind of men who would respond to His plan of salvation. All of this was foreknown and predetermined, but none of this requires a complete rigid lock of every event from the beginning of the world. People can chose whether to be a follower of God or an enemy of God. Their choice will affect their outcome, but it will not alter the predetermined plan.