It is our great pleasure to celebrate this year's (time period- i.e. annual, semi-annual) Charity Gala with you! 

Because of supporters like you, (Org Name) has been able to grow and flourish as an organization. Please join us for an evening filled with (details). All proceeds of this gala will go towards (specific cause). (Org Name) would be so grateful if you would be one of our esteemed guests at our Charity Gala held at the beautiful (location). We look forward to the honor of celebrating with you on (date).