How soon should I go to an endodontist?

I went to the dentist last week and he gave me my dental plan. Basically, my X-rays show that I might have two abscess (one on my top front tooth and one on my bottom front tooth), BUT he told me that I need to get fillings on 3 of my teeth before going to the endodontist. I'm just wondering why I would need to get the fillings before going to the endodontist and if I should just go to the endodontist first. The root of my upper tooth is really starting to hurt.