What does Acts 2:9 mean?

Filled with the Holy Spirit, 120 Jesus-followers are speaking to a crowd of people who have come to Jerusalem for Pentecost, one of the three major feasts in the Jewish calendar. Miraculously, the Jesus-followers are speaking in the visitors' native languages—languages the speakers don't even know.

The Medes, Parthians, and Elamites come from modern-day Iran while the Mesopotamians are from modern-day Iraq; all of them probably speak Aramaic. They are likely descendants of the Jews taken into exile. Around 740 BC, after generations of rebelling against God, the Northern Kingdom of Israel was taken into exile by the Assyrians. The king of Assyria took most of the Israelites to a city populated by Medes (2 Kings 17:6) and brought in people from Babylon and the surrounding area to settle in Samaria (2 Kings 17:24). The immigrants intermarried with the few Israelites left to become the Samaritans.

Between 607 and 586 BC, God sent the Southern Kingdom of Judah into exile in Babylon for their own vile idolatry (2 Chronicles 36:1–21). Seventy years later, king Cyrus of Persia allowed the Jews to return to Jerusalem (2 Chronicles 36:22–23). Not all of them did. In fact, at one point, one-third of the population of Baghdad was Jewish. Persecution slowly grew during the first half of the twentieth century and about 105,000 out of 121,000 Jews left after Israel became a nation. By the year 2000, there were barely any Jews left in Iraq. As of this writing, there are less than 10,000 in Iran.

Judea, of course, is the region between the Mediterranean Sea and the Jordan River where Jerusalem is, but in this case, it may include all the territory ruled by David, which would include Samaria, Galilee, and part of Nabatea, across the Jordan River from Judea proper.

Cappadocia is the region in the central-east portion of modern-day Asia Minor. Pontus is north of Cappadocia along the shore of the Black Sea. In this context, "Asia" is not the continent to the east of the Mediterranean Sea. Rather, this is the district that takes up much of the western edge of modern-day Asia Minor. Asia Minor is the location of the seven churches of Revelation 2—3.

Strangely enough, evangelical missions to most of these places are not recorded in the Bible. We know that Philip spent significant time in Judea and Samaria (Acts 8:4–25; 21:8) and Paul stayed in Ephesus for two years (Acts 19) and was in and out of Troas in Asia (Acts 16:8–11; 20:5–6). The spread of Christianity in present-day Iran, Iraq, Arabia, and eastern Asia Minor was significant but is only recorded in non-biblical sources.