In centuries past, churches often owned a great deal of the land that surrounded the church buildings. These lands were mostly rented out to farmers. The rents supported the priest that presided over the local parish. As times changed, many churches sold their land or it was taken from them by invaders and governments. This eventually reduced many churches to poverty as their income was lost. Churches began collecting more donations than ever before.
Parishioners that attend the local church are expected to help support it. They generally tithe a portion of their income. The donations are used to support the local church workers and maintain the buildings. Donations do not always cover the cost of maintenance. When this happens, local churches will ask their parishioners to assist with more tithes or hold fundraising events. It may take a year or two to raise enough money for maintenance, but church members are generally hard working people that will do their best for their faith.