Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of church] Members:
Words can't begin to express the gratitude I feel for all you have done more [me/for another person you are donating on behalf of]. You have been a big part of [my/person donated on behalf of] life, and I would like to take this time to give a small part of your gift to me back to you.
I have enclosed a donation for [amount of money]. I would appreciate if this gift would be used for [directions for use, such as "paying for the children to attend camp"].
Thank you again, and God Bless each and every one of you.