There are only three instances of tongues-speaking recorded in the book of Acts: 2:1-13, 10:44-47, and 19:1-7. The most extensive instance, of course, is Pentecost. On one level, speaking in tongues at Pentecost played a doxological role since the apostles and others were were testifying to God’s mighty (salvific) works. The means (foreign tongues) and content (subject matter of the speech) of tongues-speaking caused the audience to be amazed (Acts 2:5-12). When Cornelius and other Gentiles with him spoke in tongues, their content also was doxological: “extolling God” (Acts 10:46).
But testifying to God’s greatness comprises only one layer of the significance of tongues-speaking in Acts. Apparently the most important role was to demonstrate the certainty of the Holy Spirit’s arrival as the inauguration of a new age. The phenomenon of people speaking in languages they never learned was so astounding that it demanded an explanation. Luke chose the four descriptors “bewildered” (2:6), “amazed” (in both 2:7 and 12), “astonished” (2:7) and “perplexed” (2:12) to describe the audience’s reaction. Their verbal query, “What does this mean?” was exactly the response God intended. In answer to this question, Peter cited Joel 2:28-32, explaining saying that this tongues-speaking signaled that the new age of the Spirit had broken into the present order. The ascended Christ was beginning to pour the Spirit upon all flesh (2:33). Speaking in tongues was the first sign that this was taking place.
Yet there is an even more specific role of tongues-speaking in Acts. When Cornelius and others in his household (Gentiles) were converted, they too received the gift of the Holy Spirit. Clearly, Luke’s purpose in recording this account was to demonstrate that the gift of the Holy Spirit had transcended ethnic boundaries. His wording is unmistakable: “The believers from among the circumcised [Jews and possibly proselytes to Judaism] were amazed, because the gift of the Holy Spirit was poured out even on the Gentiles” (Acts 10:45, emphasis mine). And what indicated that the Spirit had been poured out? “For they were hearing them speaking in tongues and extolling God” (Acts 10:46, emphasis mine). When Peter heard the Gentile converts speaking in tongues, he rightly concluded that the Gentiles had received the Holy Spirit to the same extent and in the same way he and the other Jewish believers had. These Gentiles, too, should be baptized (10:47). Beyond indicating that the new age of the Spirit had arrived, speaking in tongues provided the litmus proof that the Holy Spirit’s pouring out had flooded beyond ethnic boundary between Jews and Gentiles (see also Eph. 2:18).
The account of the Ephesian believers speaking in tongues also demonstrates that Gentile believers could receive the Holy Spirit. But since that understanding had clearly been established back in Acts 10, Luke’s emphasis here is different. Here he is concerned to show that the Spirit only indwells those who make Jesus the conscious object of belief. The Ephesian “disciples” had been baptized into John’s baptism. Paul clarified for them the role of John’s baptism. It was merely preparatory for the coming of Jesus Christ. Only after they were baptized in the name of Jesus did they receive the gift of the Holy Spirit, evidenced by their speaking in tongues.
From the foregoing analysis, we can distill in Acts four distinct roles for speaking in tongues. The first role is doxological. Speaking in tongues brought glory to God both by the miraculous nature of the event itself, and by the content of what was being proclaimed (Acts 2:11, 10:46). The second role is eschatological. Speaking in tongues indicated that the Holy Spirit was being poured out on all flesh as the inauguration of the new age (Acts 2:16-21, 33-36). The third role is missiological. Speaking in tongues validated the spread of missions beyond the borders of Israel since the Spirit was poured out on anyone, Jews or Gentiles, who believed in Jesus (Acts 10:46-47; 11:15-18). Finally, speaking in tongues serves a soteriological role. Faith in general or faith wrongly directed is not sufficient to receive the Holy Spirit. Jesus must be the conscious focus of faith (Acts 19:1-7).