A church sale is a type of jumble sale (rummage sale) where a church typically needs funding for missions and events or even upkeep of the church, they can hold a sale of used goods donated by church members or other generous members of the neighborhood. These used items are typically what you would find in garage sale or yard sale.
The proceeds will go to the church and to fund the specific mission or event or church renovations that need to be done. The sale typically consists of members of the church volunteering their weekend free time to help the church hold the sale. The sale is usually held on weekends in church parking lots, playgrounds or any open space.
References
Church sale Wikipedia(Text) CC BY-SA