If you are a parishioner, you benefit from the staff, programs, and facilities of our parish, and they all have a cost.  But this is not the most important reason.  The most important is the following:

Giving of our time, talent, and treasure – in an intentional and calculated manner – is essential to our individual growth in holiness.  Here’s why: if we do not intentionally share our gifts, putting God and His Kingdom first, we will not be given the “higher” gifts because we have not been generous stewards of the gifts God has already given us.  God looks for generous hearts already striving to put Him and others first; and to those He will ordinarily give the “higher” gifts, because that heart is already disposed to use those higher gifts for the benefit of others.