Those who believe the true Church never changes know nothing about first-century Christianity.

Rev. Karl Rahner, the scholar, often reminded us that there have been only four basic changes in our Christian faith, and two happened within 50 years of Jesus' death and resurrection.

The first was a switch from a short-term to a long-term faith, from the equivalent of training for a 100-yard dash to preparing for a marathon.

Not returning soon

As we know from St. 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 St. Luke's Gospel and his Acts of the Apostles (written around the year 85) that we first encounter the belief that Jesus won't return during the lifetime of any of the readers.

While this short/long concept of faith was playing out, the second change was occurring: The Christian community confronted the unforeseen switch from being a Jewish group to becoming a Gentile Church.

The historical Jesus was a Jew, and all His followers were Jews. It was against the background of early first-century Judaism that this Galilean carpenter preached His reform. So how could a 100-percent Jewish community transform itself into an almost 100-percent Gentile Church within three generations?

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 Sunday'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 (Acts 2:1-11): "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 is giving concrete forms to his own experience of the Spirit. No one can live through such drastic, Spirit-inspired changes without being disturbed.

Common good

On the other hand, the Spirit also has other roles in the Church. Paul reminds his Corinthian community (I Corinthians 12:3-7,12-13), "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."

In the Sunday Gospel (John 20:19-23), 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 is just reminding them of the power they have over others for good or bad.

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.