How do I switch to being an arcanist?

I feel like an idiot for having to ask this, I have changed classes many many times before and never had this problem. I went and did all the quest to get to LL. Found the vendor that sells the beginner weapons for the classes. Purchased the lvl 1 book weathered grimoire. Then I go to equip it to change my class and it wont give me the option. If I manually move it to the weapon slot i get a error that says "unable to equip, you have not yet unlocked that class." Am I missing something here? is there a quest or something?

You have to go to the arcanist guild and do the quest there. You have to be level 10 and done the quest to switch class. They will also give a starting weapon which is what you are talking about the grimoire book.

thanks for the help