Greetings in Christ!
Congratulations on your selection as Church Treasurer!
On behalf of the leadership and entire congregation here at (NAME OF CHURCH), I also wanted to express our thanks for your willingness to take on this responsibility.
No doubt, you will face challenges along the way that seem to be more than you can handle or even beyond your capabilities. Rest assured, we will do our best to provide any needed help at that time if you need it.