Thank you for the interpretative question on Acts 13:48, “Is Acts 13.48 describing predestination?”
In looking at the previous content and the context, the meaning of the word, appointed, may imply predestination.
The text says this, “On the next Sabbath almost the whole city gathered to hear the word of the Lord. 45 When the Jews saw the crowds, they were filled with jealousy. They began to contradict what Paul was saying and heaped abuse on him. 46 Then Paul and Barnabas answered them boldly: “We had to speak the word of God to you first. Since you reject it and do not consider yourselves worthy of eternal life, we now turn to the Gentiles. 47 For this is what the Lord has commanded us: “‘I have made you[f] a light for the Gentiles, that you[g] may bring salvation to the ends of the earth.’[h]” 48 When the Gentiles heard this, they were glad and honored the word of the Lord; and all who were appointed for eternal life believed” (NIV).
Here are some thoughts for one’s consideration:
A. The message was shared with Jews and Gentiles but the Jews were jealous of Paul. They contradicted and rejected the message in hopes that the Jews and Gentiles would follow them. They couldn’t or wouldn’t accept it for that would make them followers of the message of the Apostle Paul. Jealousy drove them to dispute the message of Paul.
B. Paul and Barnabas heard their rejection of their message. That rejection would indicate that they refused the message of eternal life. They made that decision to reject it.
C. The Gentiles heard Paul and Barnabas’ message and believed it. Their acceptance indicate that they had eternal life. They chose to believe the message of Paul and Barnabas.
D. Luke who records this event see one group of people rejecting the message and another group receiving the message the Paul and Barnabas. Luke’s conclusion is that those who accepted the message were the one’s appointed by God for salvation and those who rejected the message were not appointed for salvation.
The word, appoint, in the Greek is tasso which has the idea to place in order, arrange as to appoint. It implies determined. God has so arranged the events that when the message of Paul and Barnabas was spoken, God has brought about those individuals to be there to hear and to respond to the message. The Gentiles may think that they came there on their own, but it is God who is directing the affairs of men to challenge or to accept the message of Paul and Barnabas.
In theological terms, God already knows who will be saved. There name is written in the Lamb’s Book of Life. Jesus said that he had other sheep that he must gather together to form one flock. This knowing who are his sheep implies at least preordination. There is no missing sheep nor is there one additional sheep. It is the set arranged number of sheep/believers who will believe.
Romans 8 says this about the process by God, “28 And we know that in all things God works for the good of those who love him, who[i] have been called according to his purpose. 29 For those God foreknew he also predestined to be conformed to the image of his Son, that he might be the firstborn among many brothers and sisters. 30 And those he predestined, he also called; those he called, he also justified; those he justified, he also glorified” (NIV).
This foreknowledge of God would include appointing from the beginning of his plan to bring about salvation for those individuals and its culmination with glorification. I understand that the word, appoint, refers more to the time of their salvation in history, not just the choosing of them for salvation. It was the time for those Gentiles to believe the message of Paul and Barnabas.
SUMMARY: It is the appointed time for the Gentiles to believe.