I want to know the purpose of ecchi and smut?
Why are they given?
Is it to simply arouse us readers? Or for what?

Uh... well, smut in shoujo/josei is comparable to a dirty romance novel - basically porn with romance thrown in, so it 's not the impersonal sex you get in hentai; this is probably more appealing for most girls. So basically yes, the purpose is to turn on the reader by providing sex in a different context than in hentai.

I imagine that ecchi is similar but it seems to feature more panty shots and breast flashes than actual sex (keeping in mind that I haven 't read many ecchi manga) so maybe it's less about the relationship between the characters and more about just portraying a sexy female character who readers can fantasize about. Dunno.