Of course, one thing Pentecost does is reverse the scattering that took place at Babel where languages--or "tongues"--were confused. But recently I discovered another possible background. Let me explain.
In Jesus’ day “messianic” hopes went hand-in-hand with the idea of a restoration of the tribes of Israel scattered to the nations. This is evident from numerous texts and has been observed by a plethora of scholars. In fact, the idea that God would one day restore Israel from exile is even found on the lips of Moses at the end of Deuteronomy. After first warning Israel that falling away from the covenant would mean judgment and exile, he goes on to say:
“And when all these things come upon you, the blessing and the curse, which I have set before you, and you call them to mind among all the nations where the Lord your God has driven you, 2 and return to the Lord your God, you and your children, and obey his voice in all that I command you this day, with all your heart and with all your soul; 3 then the Lord your God will restore your fortunes, and have compassion upon you, and he will gather you again from all the peoples where the Lord your God has scattered you (Deut 30:1-3).E. P. Sanders has even gone so far as to say: “In general terms it may be said that ‘Jewish eschatology’ and ‘the restoration of Israel’ are almost synonymous” (Jesus and Judaism, 97). In addition, this eschatological ingathering would include not only the Israelites but the Gentiles as well.
So there would be an ingathering of Israel from the nations. But where would they be gathered to? The answer was also clear to ancient Jews: the Temple. This is also evident in many texts. See for example Isaiah 2, which offers a programmatic vision for the restoration:
“It shall come to pass in the latter days that the mountain of the house of the Lord shall be established as the highest of the mountains, and shall be raised above the hills; and all the nations shall flow to it, 3 and many peoples shall come, and say: “Come, let us go up to the mountain of the Lord, to the house of the God of Jacob; that he may teach us his ways and that we may walk in his paths” (Isa 2:2-3).Much more could be said (believe me, my dissertation covers a lot of this ground!). In fact, the book of Acts, and especially the account of Pentecost is loaded with texts relating the fulfillment of these restoration expectations. I’ve already discussed that here.
In fact, Jesus himself is described in the New Testament as the New Temple (e.g., John 2:19-21; cf. Mark 15:38). The ingathering thus takes place as we come to Jesus.
So how do the tongues of fire fit in here?
Well, one of the most prominent passages relating a vision of tongues of fire is found in 1 Enoch 14. There Enoch is led into the heavenly temple. Here is how it is described:
“…and in the vision, the winders were causing me to fly and rushing me high up into heaven. And I kept coming (into heaven) until I approached a wall which was built of white marble and surrounded by tongues of fire; and it began to frighten me. And I came into the tongues of fire and drew near to a great house which was built of white marble, and the inner wall(s) were like mosaics…And I entered into the house… And behold there was an opening before me (and) a second house which is greater than the former and everything was built with tongues of fire. And in every respect it excelled the other)―in glory and great honor―to the extent that it is impossible for me to recount to you concerning its glory and greatness… And I observed and saw inside a lofty throne―its appearance was like crystal and its wheels like the shining sun; and I heard the voice of the cheribum; and from beneath the throne were issuing streams of flaming fire. It was difficult to look at it. And the Great Glory was sitting upon it…” (1 Enoch 14:8ff).The heavenly house is almost certainly meant to be understood as the heavenly temple. Language such as “I drew near” and the image of God’s throne were closely associated with Israel’s worship of God in the Temple (cf. Ps 11:4).
The key here is that the heavenly temple is characterized with tongues of fire.
Much more could be said about 1 Enoch, but for the simplicity of this post let’s move back to Acts 2. That the Church is the temple of God is attested elsewhere in the New Testament. Paul explicitly calls the Church the temple in 1 Corinthians 3:16: “Do you not know that you are God’s temple and that God’s Spirit dwells in you?” The idea is also found in Ephesians 2:21, which describes the Church united to Christ growing into a “holy temple”. In fact, for a great treatment of dozens of other passages relating the Temple to the Church see G. K. Beale, The Temple and the Church’s Mission: A Biblical Theology of the Dwelling Place of God (New Studies in Biblical Theology 17; Downers Grove: InterVarsity Press, 2004).
Given the prominence of the tongues of fire in the vision of the heavenly Temple in 1 Enoch―a book well-known to the early Jewish believers and even cited in the book of Jude―it seems to me that the tongues of fire in Acts may be read in terms of New Temple imagery. It would seem hard to believe the early readers of Luke would not have made the connection. Thus, Acts 2 describes how the ingathering to the heavenly Temple would be realized through the Church’s ministry. By uniting oneself to the Church one was gaining access to the heavenly temple. The Church therefore is not merely an earthly phenemona―it is heavenly.
Important support for such a reading may be found in Revelation 1-3 where one encounters a vision of Jesus in the heavenly temple, surrounded by seven lampstands, each with seven “torches” burning. We are told that “the seven lampstands are the seven churches” (Rev. 1:20). Many have also seen the seven torches as in image of the Spirit [cf. Zech 4:10; Beale, The Book of Revelation (NIGTC; Grand Rapids: Eerdmans, 1999), 189]. Warning the churches not to fall away, Christ warns those who will not hear him that he will “remove your lampstand from its place, unless you repent (Rev 2:5). The idea seems to be clear. Somehow the churches have a presence—a lampstand—in the heavenly temple. If they do not repent, they will be removed.
The heavenly dimension of the Church’s existence is even more clear in Hebrews 12.
“But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, 23 and to the assembly of the first-born who are enrolled in heaven, and to a judge who is God of all, and to the spirits of just men made perfect, 24 and to Jesus, the mediator of a new covenant, and to the sprinkled blood that speaks more graciously than the blood of Abel” (Heb 12:22-24).Note the language―not you will come to "innumerable angels...the assembly...spirits of just men made perfect...and to Jesus", but you have come. By the way, the word for "assembly" in Greek here is ekklēsia--"Church". The author says, "you have come to the Church" of those enrolled in heaven.
The tongues of fire in Acts 2 therefore seem to evoke 1 Enoch and teach us that the ingathering is taking place at the heavenly temple through the Church’s ministry.
 Sanders, Judaism: Practice and Belief, 289-98; Wright, New Testament and the People of God, 299-338; Dunn, Jesus Remembered, 393-96. Especially of note is the recent treatment by Michael F. Bird, Jesus and the Origins of the Gentile Mission (Library of Historical Jesus Studies 331; New York: T&T Clark, 2007), 26-29, which offers an extensive examination of the presence of such hopes in ancient Judaism. Bird cites a number of texts where the restoration of Israel is linked with the idea of the salvation of the Gentiles either en masse (cf. Isa 11:6-10; 42:1-12; 49:6; 66:23; Zeph 2:11; Zech 2:15; Tob 14: 6-7; T. Jud 24:6; 25:5; T. Sim 7:2; T. Dan. 5:11; T. Ash. 7:3; T. Zeb. 9:8; T. Benj. 10:5; 2 Bar 68:5; Sib. Or. 5:493-500) or as merely a remnant (cf. Jub. 2:28; T. Naph. 8:2-3; Amidah 13; 4 Ezra 3:36; 2 Bar 42:5; 72:2-6; also cf. t. Sanh. 13:2; T. Naph. 8:3-4), acknowledging and praising the God of Israel (cf. Dan 3:28-29; 4:1-37; 6:26-28; Pss. 66:1-12; 22:27-28; 46:10; 96:7-10; 117:1-2; Ezek 39:7; 2 Macc 2:28; T. Jud 25:5; Bel. 41-42; Ep. Arist 177, 187-294; Jos. And As. 15:7-8) and accepting the Law of God (cf. Philo, Vit. Mos 2:36, 43-44; Sib Or 5:264-66; 2 En. 33:9; 48:6-9). A number of texts attest to the idea of Israel’s conquering of the Gentiles (cf. Num 24:7, 17 LXX; Pss 2:8-11; 10:15-16; 22:28; 46:6-11; 47:1-9; 48:1-8; Isa 49:23; 54:3; Dan 2:44; 7:14, 27; Obad 21; Zech 14:9; Amos 9:11-12; Zeph 2:1-3; 3:14-20; Mic 5:9; 7:16-17; 1 Macc 4:11; Bar 4:25, 31-35; 4 Ezra 6:26; Jub 26:23; Sib Or 3:49; T. Jud. 24:6; T. Zeb 9:8; 1 En. 48:7-10; T. Mos 10:1-7; Pss. Sol. 17:1-34; Philo, Praem. Poen. 79, 93-97; Vit. Mos. 1.290; Tg. Isa. 30:18-33; 1 QM 1:4-5; 6.5-6; 12:10-16; 19:3-8; Josephus, B. J. 6.312). However, Bird importantly also observes that in many texts the expectation of the destruction of the Gentile nations appears alongside hope for their (partial) salvation (cf. e.g., Isa 66:15-21; 2 Bar 72:2-6; t. Sanh. 13:2; Pss. Sol. 17:22-25, 30-31). Thus, Bird rightly concludes, “views of defeat and admission of the Gentiles were not necessarily mutually exclusive."