The power of the Holy Spirit was able to do more than save three thousand people on the Day of Pentecost. The power of the Holy Spirit was able to unify those three thousand people into a community of believers. Although they came from different nations, spoke different languages and had different past expereinces, they still had the Holy Spirit in common. Paul teaches that they were many members, but part of one body. That's what we are today, many members but still part of the same body. Part of the same community of believers.