Predestination comes down to God's sovereign choice, God predestined that all who would be saved must be the righteousness of God in Christ. The promise of the gospel is that if you hear the gospel and receive it by faith, you receive the Holy Spirit and you become the righteousness of God in Christ. Some Calvinists believed that there was this book, the book of life, God wrote all the names of those who would be saved in it and that was that. Actually, every soul that comes into the world has their name written in the book of life. If you by choice become a child of perdition, your name is blotted out.
The point is predestination is not fate, it's based on the sovereign will and eternal nature of God. Now you will never be omnipotent so there are things about God's nature that cannot be communicated to us as creatures, righteousness is not one of them. You cannot make that choice apart from God's intervention in your life and heart, you must be called to repentance, hear and understand the gospel, and receive the gospel. All of which are gifts of grace, there is no other way for sinful man to approach holy God. The good news is that it is available to whosoever will.
If you fear God there is no way you committed the unpardonable sin. The people who do are children of perdition, the opposite of being born again. They are forever enemies of God, which is why they blasphemy (slander) the Holy Spirit. There is a catch, God must choose you and his decision is final. The challenge is to know what he requires to choose you, according to Peter:
To Him all the prophets witness that, through His name, whoever believes in Him will receive remission of sins.” While Peter was still speaking these words, the Holy Spirit fell upon all those who heard the word. (Acts 10:43,44)
No self respecting Calvinist would deny this, hear the gospel, receive the Holy Spirit and you are saved. That is when the Holy Spirit tells you that you are:
For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, “Abba, Father.” The Spirit Himself bears witness with our spirit that we are children of God, and if children, then heirs—heirs of God and joint heirs with Christ, if indeed we suffer with Him, that we may also be glorified together. (Romans 8:15-17)
This promise is to whosoever will, there are no exceptions.
Grace and peace,
Mark