In Harper Lee's To Kill a Mockingbird, Chapter 12, one salient difference between the church of Calpurnia and the Maycomb Methodist Episcopal Church South is that the black church allows the children, Scout and Jem, to remain whereas the white churches are strictly segregated.  Thus, the spirit of charity abounds in the poor, little church that has few hymn books and no organ or piano. 

On the other hand, the ladies of the Methodist Episcopal Church who practice charity abroad by sending missionaries and charity to Africa, help no one at home who is outside their perimeters.  Clearly, Chapter 12 points to the religious hypocrisy of the white community.

That the congregation of Calpurnia's church are poor and oppressed as well is evident when the hymns, which are sung jubilantly, end "in a melancholy murmur."  

When the preacher gives his sermon, the children notice that Reverend Sykes "used his pulpit more freely to express his views on individual lapses from grace."  The Reverend scolds the more recalcitrant of his congregation, even to the point of defining their sins.  Scout also notes that, to their amazement, Reverend Sykes chastises the church members:

....Reverend Sykes emptied the can onto the table and raked the coins into his hand.  He straightened up, and said, 'This is not enough, we must have ten dollars.'

But, then, he explains that the money is for the family of Tom Robinson.

The answer to this can be found in Chapter 12.  This is the chapter where Calpurnia has to watch the kids on a Sunday and so she takes them to the First Purchase AME Church.  The major difference is that the First Purchase Church has none of the " familiar ecclesiastical impedimenta we saw every Sunday."

What that means is the the black church was poor and could not afford to buy all the stuff the white church had.  Some things the black church lacked included a piano and organ.  The also did not have hymn books or church programs.