How Do We Say Thank You?

We should acknowledge first time givers. When someone gives for the first time, they are acknowledging that they are committed and want to be part of the congregation. A thank you note is all that is required. Asking for a giving commitment is not a good idea, but a simple thank you card is a good idea.
Acknowledging special gifts is also a good idea. The amount is not the issue but just the fact that they gave to a special need is important. If it is a large gift, directed at a specific need, it is a good idea to make the thank you a one-on-one discussion or encounter.
In neither the first-time-thank-you or special-gift-thank-you is it necessary to discuss amount or even to know the amount. People are often sensitive about the amount, but a simple thank you or thank you card is always appreciated.

