Acts 2:1-4 (NIV):
When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.
Craig Keener, Acts Vol. 1, pp. 793-94:
Yet Luke reports the Pentecost experience not merely as a matter of historical interest but because for him it set the normative pattern for the church. THis is not to say that all the phenomena of Pentecost would be repeated on subsequent occasions (he never reports the wind or fire again) but to contend that, for Luke, the church’s experiences was (or should be) pervasively charismatic; as Richard Hays puts it, it was to be not so much an expression of “early catholicism” as of “early pentecostalism” [Hays, Moral Vision, 135].
The Pentecost experience is repeated (Acts 4:31-35), including beyond Jerusalem for other groups (8:15-17; 10:44-47; 19:6), suggesting that it is paradigmatic. As Luke repeats the Cornelius story and Paul’s conversion each three times, emphasizing key turning points for the Gentile mission, he repeats glossolalia (a sign useful for Luke’s emphasis on cross-cultural speech, 1:8) three times (2:4; 10:46; 19:6). But whereas the other repetitions allude back to a key event, the repetition of this sign from the Pentecost narrative evokes that narrative through a repeated experience. Luke thus treats the Pentecost experience as paradigmatic (as in 2:38-39).
G.K. Beale, A New Testament Biblical Theology, pp. 594-95:
The appearance of “tongues of fire” (Acts 2:3) is an expression of the coming Spirit that reflects a theophany. But more can be said: it appears to be a theophany associated with the descending divine presence of the heavenly temple. A number of considerations point to this.
The report that “there came from heaven a noise like a violent rushing wind” (Acts 2:2), and that there appeared “tongues of fire” calls to mind the typical theophanies of the OT. God appeared in these theophanies with thunderous noise and in the form of fire. The first great theophany of the OT was at Sinai, where “God descended on it in fire” and appeared in the midst of loud “voices and torches and a thick cloud” and “fire”. Sinai was the model theophany for most later similar divine appearances in the OT, and to some degree God’s coming at Sinai stands in the background of the Spirit’s coming at Pentecost.
What is the nature of the miracle recorded here in Acts 2:1-4? The coming of the Spirit is joined by two manifestations: a noise in the sky, like a strong blowing wind (2:2), and divided tongues (that looked) like fire (2:3). In describing the event as accompanied by these natural phenomena, Luke is echoing the theophany scenes of the OT, in which God’s presence is accompanied by similiar signs (Exod 19:16; Judg 5:4-5; cf. Ps 18:7-15; 29:3-9).
Luke is also using the rhetorical strategy of ekphrasis, that is, employing language that appeals as much to the eye as to the ear. Theon defines ekphrasis as “bringing what is portrayed clearly before the sight.” What is portrayed could be “of persons and events and places and periods of time” (Prog. 118, trans. Kennedy 2003, 45). An ekphrasis of an event could include a description of “war, peace, a storm, famine, plague, an earthquake” (Prog. 118, trans. Kennedy 2003, 45) […] The function of ekphrasis or ekphrastic language in a narrative is often to draw attention to the significance of the even thus described for the overarching argument of the narrative (Krieger 1992, 7). Such is certainly the case with the use of ekphrastic language in Luke and Acts, in which vivid language is used at key moments in the life of Jesus. […] The ekphrastic language in the Pentecost scene underscores the continuity between the founder of the “Way” and his followers. Significant events in Jesus’ life and ministry were depicted in language that appealed to the eye more than the ear. The beginning of the disciples’ “public ministry” described in similarly vivid language, marking the disciples’ reception of the Holy Spirit.
Darrell Bock, Acts (BECNT), p. 99:
These disciples begin to speak in ἑτέραις γλώσσαις (heterais glossais), which refers to other languages, as verse 8 makes clear. In the OT, the expression appears in Isa. 28:11 LXX in the singular. This one-step understanding differs from the description in 1 Corinthians, where two steps (utterance and interpretation) are required for understanding. In Acts this speaking of tongues in foreign languages is done as the Spirit gives them utterance (so also Jervell 1998: 133-34). The term for “utterance” (ἀποφθέγγεσθαι, apophthengesthai) is relatively rare, appearing only three times in the NT, all in Acts (2:4, 14; 26:25), and six times in the LXX (BDAG 125; 1 Chron. 25:1 [positively of prophecy]; Ps. 58:8 [59:7 Eng.]; Mic. 5:11 [5:12 Eng.]; Zech. 10:2; Ezek. 13:9, 19; five of these six uses are negative, of lies or false prophets). Peter will explain in verses 17-18 that all have received the pouring out of the Spirit as an indication of the arrival of God’s promised new era (see also Luke 3:15-17, where the Spirit’s coming points to the presence of the Messiah, another point Peter makes in Acts 2:36).