This post from Desiring God called The Gospel, Not Guilt Motivates Radical Christian Giving points to a good word from Tim Keller’s book Ministries of Mercy, on the problem with using guilt as a motivation for giving.

Often books and speakers tell Christians that they should help the needy because they have so much.... But this approach is very limited in its motivating power. Ultimately it produces guilt. It says, “How selfish you are to eat steak and drive two cars when the rest of the world is starving!” This creates great emotional conflicts in the hearts of Christians who hear such arguing. We feel guilty, but all sorts of defense mechanisms are engaged. “Can I help it if I was born in this country? How will it really help anyone if I stop driving two cars? Don’t I have a right to enjoy the fruits of my labor?” Soon, with an anxious weariness, we turn away from books or speakers who simply make us feel guilty about the needy.

The Bible does not use the guilt-producing motivation, yet it powerfully argues for the ministry of mercy.

Our motivation for giving should come from the gospel as a response to the gift of Christ. You should read the whole post and check out Tim Keller's book Ministries of Mercy.