Act 13:48 Now when the Gentiles heard this, they were glad and glorified the word of the Lord. And as many as had been appointed to eternal life believed.

Calvinists often try to use Acts 13:48 to point to their concept of predestination. But this is just not the prooftext which they need. The context says nothing about fatalism, instead it is about people responding to preaching. As with any language, the text supports multiple translations. In this case, the verb “had been appointed” could just have easily have stated “appointed themselves”. This would turn the verse from a prooftext for Calvinism into a death knell for Calvinism:

Act 13:48 Now when the Gentiles heard this, they were glad and glorified the word of the Lord. And as many as appointed themselves to eternal life believed.

Jesse Morrell explains why the context better fits the reflexive translation than the NKJV rendering:

3. Also notice the passive/middle ending “μένοι.” That means that ordained/disposed can be taken as something which was done to them (passive), in this case by the word, or something which they did to themselves (middle), in this case by allowing themselves to be properly influenced by the word. Given the context of this passage, especially in contrast with vs. 46 that uses the reflexive pronoun “ἑαυτοῦ” to say that they judged themselves unworthy of eternal life, this verb “τεταγμένοι” should be understood to be in the middle voice. Context is the only key in determining whether a verb is in the passive or in the middle, as the ending is identical.

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So with the imperfect indicative verb “ἦσαν” and the perfect middle verb “τεταγμένοι”, this passage is saying that those who believed were those who had continually disposed themselves to eternal life in the past, when the word was presented to them by Paul and Barnabas.

This understanding of the verse would make a lot of sense in the context of Paul’s ministry. Paul had a very hard time converting outsiders. Instead, Paul’s main body of converts came from the God-fearers. These were Gentiles who worshiped God but were too weak to undergo the critical conversion to Judaism via circumcision. The text would be saying that Paul captured this market of ready believers. This stirs up the Jews against Paul. Paul was stealing their converts into a religion that appalled them:

Act 13:50 But the Jews stirred up the devout and prominent women and the chief men of the city, raised up persecution against Paul and Barnabas, and expelled them from their region.

This fits Paul’s previous persecutions. Acts 13:49 is saying Paul converted the God-fearers.