I have just completed a postgraduate course, in which I studied Category Theory, without having a background in Set Theory and Logic - this probably already sounds absurd to many. This did not seem to be a problem - at least until now.

As a (reasonable, I thought) progression to my studies, I am trying to teach myself Topos Theory. Until the notion of geometric morphisms, I thought it might be ok to just omit the Logic examples from my studying. And it worked fine, I could keep up with learning. But I have now arrived to the concept of a classifying topos. It feels that now my lack of knowledge in Logic is going to be a very big obstacle. It seems almost impossible to continue. I am worried that this was a big mistake from the beginning. So I am asking the Topos theorists that read this, for their opinion on how stupid they think I have been by thinking in this way, and maybe what is the best way/source to learn what is needed. Thanks for any help.