How important the content regarding text? - Doesn't make sense to me.
The spider is not that smart or is it? - Umm, yes. Google spend billions developing search technology and have some of the most amazing software engineering minds around.
How can the
spider understand what your trying to say and put a relevant to what
your site is understanding your key words are in the text and meta
tags? - Well seeing as META keywords are useless for the Google. They don't use them.
The way the search technology works? I suggest reading here about
Google's Algo patents.
KP