Albert Barnes Commentary Acts 2:4

"And they were all filled with the Holy Spirit, and began to speak with other tongues, as the Spirit gave them utterance." — Acts 2:4 (ASV)

Were all filled with the Holy Ghost. They were entirely under His sacred influence and power (Luke 1:41, 67).

To be filled with anything is a phrase denoting that all the faculties are pervaded by it, engaged in it, or under its influence: (Acts 3:10) Were filled with wonder and amazement; (Acts 5:17) Filled with indignation; (Acts 13:45) Filled with envy; (Acts 13:52) Filled with joy, and with the Holy Ghost.

Began to speak with other tongues. In other languages than their native tongue. The languages which they spoke are specified in Acts 2:9-11.

As the Spirit gave them utterance. This means as the Spirit gave them power to speak. This language plainly implies that they were now endowed with a faculty of speaking languages they had not learned before. Their native tongue was that of Galilee, a somewhat barbarous dialect of the common language used in Judea, the Syro-Chaldaic.

It is possible that some of them might have been partially acquainted with Greek and Latin, as both languages were spoken among the Jews to some extent. However, there is not the slightest evidence that they were acquainted with the languages of the different nations specified later. Various attempts have been made to account for this remarkable phenomenon without supposing it to be a miracle.

But the natural and obvious meaning of the passage is that they were endowed by the miraculous power of the Holy Ghost with the ability to speak foreign languages—languages previously unknown to them. It does not appear that each one had the power of speaking all the languages specified (Acts 2:9–11). Instead, this ability was among them, and together they could speak these languages, probably some speaking one language and some another. The following remarks may perhaps throw some light on this remarkable occurrence:

1. This ability was predicted in the Old Testament (Isaiah 28:11): With another tongue will he speak to this people. Compare to 1 Corinthians 14:21, where this passage is expressly applied to the power of speaking foreign languages under the gospel.
2. It was predicted by the Lord Jesus that they should have this power (Mark 16:17): These signs shall follow them that believe—they shall speak with new tongues.
3. The ability to do it existed extensively and long in the church: (1 Corinthians 12:10–11) To another divers kinds of tongues; to another the interpretation of tongues: but all these worketh that one and the selfsame Spirit; (1 Corinthians 12:28) God hath set in the church— diversities of tongues; (1 Corinthians 12:30; 1 Corinthians 14:2, 4, 5, 6, 9, 13, 14, 18, 19, 22, 23; 1 Corinthians 14:27, 39). From this it appears that the power was well known in the church and was not confined to the apostles. This also may show that, in the case in Acts, the power was conferred on other members of the church as well as the apostles.
4. It was very important that they should be endowed with this power in their great work. They were going out to preach to all nations; and though the Greek and Roman tongues were extensively spoken, yet their use was not universal, nor is it known that the apostles were skilled in those languages. To preach to all nations, it was indispensable that they should be able to understand their language. And it was necessary that they should be endowed with the ability to speak them without the slow process of being compelled to learn them.
5. One design was to establish the gospel by means of miracles. Yet no miracle could be more striking than the power of conveying their sentiments at once into all the languages of the earth. When it is remembered what a slow and toilsome process it is to learn a foreign tongue, this would be regarded by unbelievers as one of the most striking miracles ever wrought in the establishment of the Christian faith (1 Corinthians 14:22, 24, 25).
6. The reality and certainty of this miracle are strongly attested by the early triumphs of the gospel. That the gospel was early spread over all the world—and that, too, by the apostles of Jesus Christ, by men from Galilee—is the clear testimony of all history. They preached it in Arabia, Greece, Syria, Asia, Persia, Africa, and Rome. Yet how could this have been accomplished without a miraculous power of speaking the languages used in all those places? Now, it requires the toil of many years to speak foreign languages, and the recorded success of the gospel is one of the most striking attestations to the fact of the miracle that could be conceived.
7. The corruption of language was one of the most decided effects of sin, pride, and ambition, and the source of endless embarrassments and difficulties (Genesis 11). It is not to be regarded as wonderful if one of the effects of the plan for redeeming humankind should be to show the power of God over all evil, and thus to furnish striking evidence that the gospel could meet all the crimes and calamities of humanity. And we may add,
8. that from this we see the necessity now of training men who are to be missionaries to other lands. The gift of miracles is withdrawn. The apostles, by that miracle, were simply empowered to speak other languages. That power must still be possessed if the gospel is to be preached. But it is now to be obtained, not by miracle, but by slow and careful study and toil. If this power is to be possessed, they must be taught it; they must labor for it. And as the church is bound (Matthew 28:19) to send the gospel to all nations, so it is bound to provide that the teachers who shall be sent forth are qualified for their work. Hence, this is one of the reasons for the importance of training men for the holy ministry.