I love my atheist brothers and sisters but I do believe that atheism is a major sin and a terrible mistake. I don't try to indoctrinate anyone, though.
Anyway, if you can speak Spanish, I strongly recommend this guy:
My thoughts on the subject: the universe didn't happen by chance, there is a higher intelligence running things; luckily for us, that creator is kind and merciful (all natural things are good). If so, it's only logical that we should praise Him and be thankful for what we've got (which is quite a lot actually).