Fear God? But I love God.

I dont understand why people say "you should fear God." What am I suposed to be fearful of? I have my full trust in God, I let him guide me in every situation good or bad. I thank him for everything I have, ask him to open peoples eyes to him. I talk to him like my friend, like my Father. Why am I suposed to fear him when I trust him so much? Maybe when people say "fear God", they mean fear not following him? Is that is? Because I can not see myself fearing him.