Saul of Tarsus was a persecutor of Christ's church. When Christ revealed Himself to Saul, this was the fulfillment of Our Father's predestination of Saul, who (as all true believers are) was chosen since eternity. As it is written, "Many are called, but few are chosen."
The Apostle Paul taught this lesson many, many times.
Now, any good Calvinist knows that whoever is called must be chosen. That verse does not fit Calvinism.
Even so, come Lord Jesus