Those who believe the true church never changes know nothing about first century Christianity.
The late Karl Rahner often reminded us that there have been only four basic changes in our Christian faith, and that two of them happened within fifty years of Jesus' death and resurrection.
The first was a switch from a short term faith to a long term; from the equivalent of training for a 100 yard dash to preparing for a marathon. As we know from Paul's earliest letters, Jesus' first followers presumed he was going to return in the Parousia in a relative brief period of time. Some in his Thessalonian community, for instance, appear to have believed none of them would die before Jesus' Second Coming. It's only when we read Luke's gospel and his Acts of the Apostles (written around 85 CE) that we first encounter the belief that Jesus won't return during the lifetime of any of the evangelist's readers.
While this short/long concept of faith is playing out, the Christian community is also having to confront the unforeseen switch from being a Jewish church to becoming a Gentile church. The historical Jesus was a Jew, all his followers were Jews. It was against the background of early first century CE Judaism that this Galilean carpenter preached his reform. How could a 100% Jewish church transform itself into an almost 100% Gentile church within three generations?
Did biblical Christianity have a John XXIII leader who guided them through this tumultuous period? Though heroic figures like Peter and Paul were on the cutting edge of both changes, our sacred authors tell us the real guiding force in those days was the Holy Spirit.
That's why today's Pentecost celebration quickly came into existence. It was both a way to sing the praises of the force behind change and a reminder to the community that no one can imitate the faith of Jesus without giving himself or herself over to the Spirit of Jesus.
With these two basic changes still creating problems for some in his church, Luke's description of the Spirit's Pentecost arrival is very significant. "Suddenly from up in the sky there came a noise like a strong, driving wind which was heard all through the house where they were seated. Tongues as of fire appeared which parted and came to rest on each of them." There's no gentle dove here, hovering peacefully over the community. The Spirit's arrival is accompanied by the disturbing images of wind, noise and fire.
Luke's simply giving concrete forms to his own experience of the Spirit. No one can live through such drastic, Spirit-inspired changes without being disturbed.
Yet, on the other hand, the Spirit also has other roles in the church. Paul reminds his Corinthian community, "To each person the manifestation of the Spirit is given for the common good." The same Spirit which creates havoc also is a force of unity. "It was in one Spirit that all of us, whether Jew or Greek, slave or free, were baptized into one body." Divisive elements are molded into one, unified force by the Spirit's power.
John tells us on what this unity is built. "Jesus breathed on them and said, 'Receive the Holy Spirit. If you forgive someone's sins they are forgiven; if you hold them bound, they are held bound.'"
We presume Jesus never wanted any of his followers to withhold forgiveness. He's just reminding them here of the power they have over others for good or bad. John's Jesus informs us that the most important daily element of the Spirit's presence in our lives is forgiveness; the thing many of us find the most difficult to offer. Yet no Christian community can exist without that element, just as they can't exist without the Spirit.