The Body of Christ

I have heard a lot of people talk about the church and whether it is important to attend. The question is what exactly is the church? Is it a building where people fellowship or is it something else? How important is fellowshipping with others? I’ve also came across people who feel that there are no other disciples but those who Jesus chose back in the biblical times and preachers and teachers today are not. There may be a few who believe that only Jesus was the only chosen one to preach the gospel. So the question is are there people called by God or was Jesus and/or the disciples who chose are the only ones chosen to preach and teach?