Under the provisions of the Finance Act 2001, income tax payers who are self-assessed or who pay part of their income tax as PAYE and part as self-assessed get relief on their donations to charities in certain circumstances. This applies, for example, to people who are farmers, C2 registered contractors, or other business owners, as well as people who may have a part-time employment along with their own business.
So when a person in this category donates at least €250 to the parish over the course of the year using the numbered collection envelopes, they will get a receipt from the parish at the end of the year. The person who prepares their tax return treats the amount of their donation to the parish the same as an ordinary expense. So the amount of income tax they will have to pay is reduced.
For example, a farmer who pays tax at 20% who donates €450 to the parish collections will save the €90 they otherwise would have to pay as income tax (so the donation only costs them €360). A farmer who pays tax at 41% who donates €550 to the parish collections will save the €225.50 they otherwise would have to pay as income tax on that amount (so the donation only costs them €324.50).
So, finally, Catholics can get some material credit in this life for their support of their parishes!