This is a question I get regularly. Many times, a Pastor will give a challenge for Christians to "test God" according to Mal. 3 and tithe for 90 days and see how God is faithful. Lots of people will indicate that they are going to participate and never give.
Why does this happen? Simply put, if you don't have a solid follow up plan, the results will be minimal.
While giving is of course a spiritual act, the encouragement of a good follow up plan helps those who made the decision to begin giving continue to give and experience God's blessing and provision.