In free will vs. predestination, both are true.  It is just one of those divine mysteries we cannot understand and that we just have to accept by faith, because both are in the Word.

It's like this...

On the outside of the door to heaven is written, "WHOSOEVER WILL."

By his free will, one enters, then finds on the inside of the door is written, "CHOSEN BEFORE THE FOUNDATION OF THE WORLD."

Romans 9 elaborates on this mystery:

14 What shall we say then? There is no injustice with God, is there? May it never be! 15 For He says to Moses, “I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion.”  16 So then it does not depend on the man who wills or the man who runs, but on God who has mercy. 17 For the Scripture says to Pharaoh, “For this very purpose I raised you up, to demonstrate My power in you, and that My name might be proclaimed throughout the whole earth.”  18 So then He has mercy on whom He desires, and He hardens whom He desires.

19 You will say to me then, “Why does He still find fault? For who resists His will?” 20 On the contrary, who are you, O man, who answers back to God? The thing molded will not say to the molder, “Why did you make me like this,” will it? 21 Or does not the potter have a right over the clay, to make from the same lump one vessel for honorable use, and another for common use? 22 What if God, although willing to demonstrate His wrath and to make His power known, endured with much patience vessels of wrath prepared for destruction? 23 And He did so in order that He might make known the riches of His glory upon vessels of mercy, which He prepared beforehand for glory, 24 even us, whom He also called, not from among Jews only, but also from among Gentiles.