I think writing the Red Work Series of Courses has been the best thing I've ever done in my life. As I go back over the things I've learned so far and try to find a way to put it into meaningful words, I keep on finding all these cool things I picked up and forgot about over the years. It's so cool.
I'm writing the Elemental Hierarchy lesson for the Black Work course now, and it's amazing. Things I thought I understood years ago are making so much more sense now when I go back over them from my current perspective. Agrippa writes about things that are fascinating after you've been initiated into the Spheres and spent some time Working with the things he talks about, but until you have, it's boring, complicated, and confusing. So much of his writing is referential to the actual experiences of a magician that I have no doubt that he was a practitioner and not just an occult journalist. His detailed understanding of how things work in the occult arts can only be explained by direct experience.
The first time I read through his stuff on the Elements, in the First Book of Occult Philosophy, chapters ... uh, three through nine, I just didn't get it. I understood the words, and I thought I grasped the concepts. I could read a correspondence table and understand the implications and the logic behind the linkages between things, but I didn't have that gnosis, that knowledge that comes from experience to make it all really click.
After actually experiencing the three levels of the elemental spheres, the cardinal, fixed, and mutable aspects of each element, it makes perfect sense. Gates, Forces, and Manifestations. It took me years to understand what Agrippa says so plainly. It's like someone says, "Put slot A in tab B," it's simple instructions, but until you understand tabs and slots, you won't understand what he's saying. But now I get it. Neat stuff, really neat stuff.
Anyway, for those like me going through this Great Work thing on their own, read, apply, and then go back and re-read is my advice. Helps put things into perspective a lot. I keep finding myself saying, "Oh, THAT'S what he was talking about!" as I go back over the basics.