Be direct

Action follows confidence.
   ... Confidence that you have a solution.
   ... Confidence that the success of your solution involves participation.

You can write it like this:
"People say they value this program because it makes a difference. Won't you consider joining us with a contribution today?"

Or like this:
"You value this program. It makes a difference. Your contribution matters so much."

The second version speaks directly to the reader. It's action oriented. And it leads right to your follow up... to your great reason why their contribution makes a difference.

Copy can make or break the confidence level of your appeal. Since you're already out on a limb to make your goals, you may as well be confident about it. You'll raise more money.