The reason that I didn't include the div. text was the wordpress. They were marking with red color the "div." text and a message on the screen was saying the div. is overqualified and I thought it wouldn't work.
Ah, yes. That warning must be ignored in this case because of how CSS specificity works. I think the warning notes are great, but sometimes you do need to go against them to make things work with the other CSS that' gets loaded by WordPress.com themes.
If a new question comes up can I ask you again directly to this forum?
If you have new questions about CSS, you should make a separate, new help request at http://en.forums.wordpress.com/forum/css-customization/#postform
I went to the post's code and I added: <!--more--) to the point where I want the text's break but it still shows all the text.
The more tag doesn't change anything for a post by itself, only when the post is displayed in a list of posts. You currently don't have a "blog" or "posts" section setup to display a list of posts.
If you're not going to setup a blog on your site or use a "posts page," then you probably want to use pagination instead of a more tag. Try switching back to using a page and follow this instead: