Here's the Web page on eBay where this postcard is for sale. There's no indication of how old the card is, but it appears to have been published before the 1920s.
It's clearly recognizable as the modern Calvary Baptist Church in downtown Darien, but back then it was a Methodist church, according to the postcard.
Here's the message on the back (it wasn't stamped, and other postcards are referred to, so it was probably sent in an envelope with a number of others):
Dear Mrs. Belden,
You see, I haven't forgotten you. I'm writing to Mary to day. I saw these cards so I am sending them. You probably have them. I found the one of Savannah among them so I am sending it along.