Spring really is a collection of 20+ projects. The overall Spring architecture is represented by this diagram
This is not complete, but gives you an idea of where things lie.
If you want to learn Spring, it is essential to learn AOP, Aspects, everything in the Core Container and the Tests layer. Learning these things gives you the grounding to learn everything else. You should then make yourself familiar with all the other 20+ projects. You should know what each project does and where you can apply them. You don;t need to learn them in detail. You only need to learn them in enough detail so you can decide that where the project will be useful. You should only learn the projects that you really need to. It's very difficult to learn all the Spring projects in great detail.
I bet there are some Spring Gods who know all the Spring projects in detail. I haven't met any of those Gods. Personally, I learn what I need when I need it.