That is only one instance, in which God may have chosen Paul. That does not automatically mean that God predestinated all believers to believe.
Instances in the scriptures are given for EXAMPLES to us. Why deprive yourself of them? Why the resistance to these great truths?
Paul was definitely chosen by God, there's no 'may have been' to it:
15 But the Lord said unto him, Go thy way: for
he is a chosen vessel unto me, to bear my name before the Gentiles and kings, and the children of Israel: Acts 9
Paul was predestined, just as we all are:
28 And we know that all things work together for good to them that love God, to them who are the called according to his purpose.
29 For whom he did foreknow,
he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.
31 What shall we then say to these things? If God be for
us, who can be against
us? Ro 8
23 And that he might make known the riches of his glory on the vessels of mercy, which he had
afore prepared unto glory,
24 Even us, whom he hath called, not of the Jews only, but also of the Gentiles? Ro 9
4 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
5 Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, Eph 1