In Acts 13:14-41, Paul speaks in a synagogue in Psidian Antioch and proclaims Jesus as the promised Messiah. When he finishes the people plead for him to tell them more (Acts 13:42-43). The next Sabbath nearly the whole city assembles (Acts 13:44). As Paul preaches, key synagogue leaders reject the gospel (Acts 13:45-47); however, many Gentiles accept it—“as many as were ordained to eternal life” (Acts 13:48).
There are three key questions that have to be addressed in seeking to understand v. 48: 1) what does the word “ordained” mean; 2) by whom were they ordained; and 3) on what basis were they “ordained.”
First, most scholars agree that the word “ordained” means “appointed,” and that is certainly the ordinary sense of the word (see Acts 15:2; 22:10; 28:3). Since nothing in the text or context requires a different sense, we should go with the ordinary sense.
Second, the text does not say who appointed them to eternal life. The grammar requires only that their appointment took place before they believed. The options for who appointed them to eternal life include God, themselves, or both God and themselves. All three are possible theologically.
God: According to Rom. 8:29, God predestined those whom he foreknew [would believe] to be like Jesus. Eph. 1:4 teaches that God chose those [He foreknew would be] in Christ to be holy and blameless. Since God knows all things, He knew who would believe in Jesus and appointed them to receive eternal life (cf. John 6:40; 1 Pet. 1:1-2).
Themselves: 1 Cor. 16:15 speaks of the house of Stephanas appointing themselves to the service of the saints. Given this NT usage, we could understand that the Gentiles’ appointed themselves to eternal life by their attendance upon and acceptance of the gospel
Both: I’m inclined to think the “both” option makes the best sense since the context highlights both divine grace and human choice. In addition to the fact that God has ordained that all who believe shall be saved, the context highlights God’s grace in the Gentiles’ interest in and attendance at the preaching of the gospel (Acts 13:42, 44). Such interest testifies that God’s grace had been at work to incline their hearts to the gospel (Acts 13:43; cf. Phil. 2:13).
On the other hand the Gentile’s choice to hear and receive the gospel is emphasized in contrast to the Jews’ choice to reject it. Notice what Paul says in v. 46 about the Jews who rejected the gospel: “you are judging yourselves unworthy of everlasting life….” By rejecting the gospel, the Jews were judging or pronouncing themselves unworthy of eternal life. Their unworthiness was a function of their own choice. By choosing to seek, listen to, and accept the gospel invitation, the Gentiles cooperated with God’s prevenient grace and appointed themselves to eternal life. In this way, they vindicate the justice of God’s prior (in eternity) appointment of them to eternal life.
Third, the basis upon which they were appointed to eternal life is implicit in the text. With regard to their self-appointment the basis was their desire to respond to God’s drawing grace. With regard to God’s appointment of them, the basis was His (fore)knowledge of their acceptance of Christ.
In sum, all those God foreknew would believe He has appointed to eternal life. People appoint themselves to eternal life by responding to God’s saving grace as it comes to them.
As an interesting parallel, the word “unworthy” occurs in a similar context in Matthew 22. Jesus tells a story of a king who invited people to the marriage feast of his son. The people, however, refused his invitations and murdered his servants. In response, the king sent out his armies, destroyed the murderers, burned up their city, and said “The wedding is ready; but they which were bidden were not worthy” (Matt. 22:8). The fact that the King sent his invitees multiple invitations indicates that the King genuinely intended for them to come. Their unworthiness, like that of the Jews in Acts 13:46, was a function of their choice. In contrast, those who were gathered from the highways and hedges to the wedding feast were called “chosen” (Matt. 22:14). Their “chosenness” came both from the King’s invitation and their response to it.