"For consider your calling, brethren, that there were not many wise according to the flesh, not many mighty, not many noble; but God has chosen the foolish things of the world to shame the wise, and God has chosen the weak things of the world to shame the things which are strong, and the base things of the world and the despised God has chosen, the things that are not, so that He may nullify the things that are, so that no man may boast before God" (I Corinthians 1:26-29).
There is no school for preachers. One preacher trains men to teach the Gospel. "The things which you have heard from me in the presence of many witnesses, entrust these to faithful men who will be able to teach others also" (II Timothy 2:2). See Professional Preachers for additional information.
This preacher you've encountered is trying to use his education as a club to intimidate you. So, let's look at Cornelius and see if his conversion supports Calvinism.
John Calvin taught that men were totally depraved and, therefore, cannot be saved unless God first initiates a change in a person. But we are told that God considered Cornelius to be a devout man who feared God prior to his learning the Gospel (Acts 10:1-4). The preacher you were talking to ignored this important point. But let's move on.
Was Cornelius selected by God to hear the Gospel? Obviously he was chosen because an angel was sent to tell him to call for Peter (Acts 10:3-6). Why did God pick Cornelius? Because his "prayers and alms have ascended as a memorial before God" (Acts 10:4). The choice was based on Cornelius' prior choice to serve God. The choice did not make Cornelius saved. Instead, he was told to call for Peter to receive instruction (Acts 10:30-33). As a result of the teaching, he was commanded to be baptized (Acts 10:47-48).
Why did God select Cornelius? God needed to break the ice so that Gentiles would be taught and brought into the church. Did every Christian have an angel sent to point out who should teach them the Gospel? I hope that would clearly false. Peter later said, "But we believe that we are saved through the grace of the Lord Jesus, in the same way as they also are" (Acts 15:11).
How then were other Christians saved?
- Christians are saved by grace (Acts 15:11; Ephesians 2:5).
- Christians are saved by faith (Ephesians 2:8).
- Christians are saved by confession (Romans 10:8-10).
- Christians are saved by repentance (Acts 3:19).
- Christians are saved when they repent and are baptized (Acts 2:38).
Did Cornelius experience things which were common to other Christians?
- Cornelius received grace (Acts 15:11)
- Cornelius believed (Acts 15:7)
- Cornelius was granted the opportunity to repent (Acts 11:18)
- Cornelius magnified God, thereby confessing (Acts 10:46)
- Cornelius was baptized in water (Acts 10:47-48)
All of this resulted from Cornelius and his household hearing the word of God (Acts 10:44; 11:13-15). The means by which Cornelius was saved, was taught in the word of God.
Was Cornelius predestined to adoption as a son (Ephesians 1:5)? Yes. It was the same way all Christians are predestined -- according to the intention of God's will. It is not an individual election to be saved but a predestined plan to save mankind that various individuals heeded.