Something we take for granted today was still a hot, debated topic when Luke composed his gospel and the Acts of the Apostles. We presume anyone can be a follower of Jesus. Race or social status make no difference. We need only have faith in Jesus. Christianity is its own religion, not a branch of any other faith.
There's just one problem. Christianity didn't start that way. In the beginning - immediately after Jesus' death and resurrection - all Jesus' followers were Jews. Unlike ourselves, they looked at Jesus as a reformer of Judaism, not as the founder of a system of faith distinct from Judaism. Being Jewish was essential to being Christian. That's where the Holy Spirit stepped in.
From Acts and Paul's letters, we know this Jewish requirement was eventually challenged by some liberal disciples of Jesus. This handful of radicals began teaching that anyone could be baptized into the faith of Jesus without first being required to convert to Judaism.
The historical Jesus had no other choice but to express his faith in the context of Judaism. Except on rare occasions, he remained in that context. That's why it was hard for some of his followers to step outside Judaism and begin to share his faith with people who didn't know the difference between a lox and a bagel. These non-Jews lived their lives in circumstances and traditions quite different from that of a Galilean carpenter. Why should they be required to accept Jesus' context before they accepted Jesus' faith?
The key element in changing peoples' minds about the context/faith issue seems to have been the insight that Christians followed the risen, not the historical Jesus. Everyone knew a free, Jewish man died on Golgotha at 3:00 o'clock on Good Friday afternoon. But, as Paul reminded his Galatian community, the "new creation" which rose on Easter Sunday morning was just as much a slave as free, just as much Jew as Gentile, and just as much woman as man. People from any culture, social status, or even gender can identify with him/her. Jesus left his historical context in the tomb and rose into ours.
Since the early church carried on the ministry of Jesus, it was guided by the same Spirit which had guided him. This Spirit eventually led them to take the humongous step of baptizing Gentiles as Gentiles.
That seems to be one of the reasons Luke mentions the native lands of the people gathered in front of the house in which the disturbing wind, noise and fire occurred on Pentecost Sunday. All were Jews, but most lived in non-Jewish places. "We are Parthians, Medes, Eleamites ... "They're amazed to hear these newly-Spirited Christians ". . . speaking in our own tongues of the mighty acts of God." Luke employs this phenomenon as an introduction to his theology that the risen Jesus can eventually be proclaimed in all cultures. No longer does one have to speak Hebrew or Aramaic in order to be among Yahweh's chosen.
Though crucial parts of Paul's I Corinthians passage have been omitted from today's liturgical selection, one classic line has been included: "To each individual the manifestation of the Spirit is given for some benefit." Jesus' Spirit enlivens all his followers. But this gift isn't just for the benefit of the person who possesses it. It somehow benefit's the whole community. We're gifted in order to be a gift for others.
John's theology of the Sprit dovetails with Paul's. If Jesus didn't send us out as God sent him out, we wouldn't need the Spirit. It's an essential part of our carrying on his uncharted risen ministry.
Thankfully the early Church left some traditions behind and gave itself over to a Spirit who guided them down those uncharted roads. Had it insisted on maintaining its Jewish traditions, almost no Gentile would even have considered jumping through the cultural hoops demanded of Jesus' followers.