The parish can get gold in diverse ways. The parish gets a percentage of gold from all the goods that players buy and sell at its market, as well as a small amount of gold from the parish tax rate set by the steward. The parish steward can also use the parish army to raid gold from other capitals.
The parish tithe rate is deducted from your villages in the parish once a day. If you return to your village and find yourself with less gold than you had before, a high parish tithe may be the reason! Consider asking your parish steward to lower the tithe rate!