My area of specialty has been geophysics for the last fifteen years, but I have been increasingly drawn toward mathematics, not the pure sort but the sort inspired by physics. Things like investigating the mathematical structure of physical theories and looking for connections between them. Toward that end, I decided to do some retraining/retooling, but I keep getting ambivalent about which books to read, which is a problem because books of this nature take a long time to work through! Specifically, I've been skipping back and forth between Hassani's Mathematical Physics, Frankel's Geometry of Physics, and Choquet-Bruhat's Analysis, Manifolds, and Physics. The problem is that each of these books has pros and cons, and that I cannot, I think, master what is in all of them. I am looking for a solid basis for pursuing more mathematically inclined physics, but I need a geodesic path to it. I cannot read a million books. What would constitute this "mathematical core"? And how can I make myself stick to a course of study instead of zigzagging all over the place? To be extra clear, it's not that I cannot concentrate, it's that I keep weighing the benefits of this or that book!