CSS

You want that the content is hidden and the you need to press the title to go to the post page or you want to un-hide the post when you pres? The second one needs JavaScript and I don't know how to it. The first one is simple:

Add something like:

.post-body entry-content {
  display: none;
}

BUT I DON'T ADVICE IT! DON'T USE THIS UNLESS YOU ARE REALLY NEEDING!

Because I think that isn't correct, and you will have problems because this applies even inside the blog post, see this site instead, that may give you some help (link).

EDIT: Link fixed

Even better, I found a better way to do it from Blogger help: (link).