Acts 2:5

Now there were dwelling at Jerusalem Jews, devout men, from every nation under heaven.

'DWELLING AT JERUSALEM'-Permanently and temporarily.

'DEVOUT MEN, FROM EVERY NATION UNDER HEAVEN'-'it characterizes them as the best of the adherents of the Jewish religion. They were so anxious to avoid offending God, that they travelled, some of them, thousands of miles to attend the feast at Jerusalem, just as the O.T. prescribed.' (Reese p. 50) 'The Jews were scattered over the Roman Empire at this time, and only the "devout" ones would make the long journey to Jerusalem to keep this feast.' (Boles p. 34)

Points to Note:

Even though the Law of Moses had been given some 1500 years earlier, including the command to assemble and celebrate Pentecost (Leviticus 23:2; Leviticus 23:15 ff). Time and culture didn't alter or change His requirements. They only ceased to be binding, when God informed us that. New Covenant, with new laws had been established (Colossians 2:14).

'Feasts like Pentecost attracted thousands of pilgrims. We are told that when Titus besieged Jerusalem (68-70 A.D.), an event which occurred about Passover time, there were no less than three million people in the city.' (Reese p. 50)