Let me be clear about what you are saying…. Do you mean that before Paul could be obedient (enabled for his true purpose), he had to profess his faith in a risen Savior? Do you mean that in order to be obedient (enabled), Paul had to have a change of heart? If so, I agree, and he did…. However, the means that brought about those changes in Paul and the total reversal of his character were extraordinarily miraculous, don‘t you think? He was a smart man, well-educated in the Old Testament scriptures; but before that remarkable day on the road to Damascus, he was spiritually blind and needed a supernatural spiritual awakening. Why was he chosen? Consider the possibility that our Father knew him very well in the spiritual realm before the foundation of the world and had a reason for His choice. I’m certain that the spiritual man in Paul loved God. I won’t presume any more than that, except to say that Scripture teaches this:
Romans 8:28-30
And we know that all things work together for good to those who love God, to those who are the called according to His purpose. For whom He foreknew, He also predestined to be conformed to the image of His Son, that He might be the firstborn among many brethren. Moreover whom He predestined, these He also called; whom He called, these He also justified; and whom He justified, these He also glorified.
In this present age, Paul taught as the Holy Spirit inspired—salvation by grace through faith (Ephesians 2:8-10); that’s how we are saved, but not necessarily the reason. i think maybe it’s because God loves His creation and wants to be surrounded throughout eternity with those who also love and revere Him. Paul finished faithful, still loving God in spite of all his difficulties—sustained by grace through every hardship until the end—as will all of God’s elect. Jesus promises.
John 10:28-29
And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand. My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of My Father’s hand.