The amount of content in the feed itself is very short:
By Jeff Kurrus A couple of months ago, I sat on a literary panel for my upcoming children’s book, Have You Seen Mary? The topic was on writing, publishing, and the behind-the-scenes of each, and myself and four other writers and publishers discussed these subjects in front of about 40 ...
As Mike said, the feed itself only contains a small portion of the original content. This is typical for news feeds because they want you to visit the original site to read the entire thing.
I just tested that feed. The entire content of the feed is already posted without any special configuration. There is nothing more you can do to capture more content... aside from asking the owner of the feed to include more content with each item.