How to efficiently study and learn Economics? I read there are a couple of questions asked in this regard, but I am not quite satisfied with the provided answers.

I am currently doing my master's degree (expecting to pursue a PhD) in Economics, and I have been very exposed to the Mas-Colell and the book of Advanced Macroeconomics by David Romer. Just reading the books, and taking notes, I end up rewriting each book myself again. 

Therefore, I want to ask what it means to you to study Economics, how is it possible to learn economics, without actually memorizing (since I think that is my problem, I try to memorize everything)? What is an efficient way to take notes (in class or from the textbook), going through the textbook and actually understanding what is being exposed? 

I hope my question is appropriate for this space, just to have a little discussion if there was someone who went through similar while pursuing graduate studies.
I am a ph.D Student in Economics, and I am sharing my experience.

It is not necessary to be able to prove everything. Each time you will have to tackle a specific issue you will have to go back to handbooks and articles that have been made.

I think what is important to memorize is the global story of each chapter of these kinds of handbooks (as Mas Colell for instance). The most useful things to memorize is probably the tool you will constantly use in Microeconomics (such as optimization, linear algebra, topology), Econometrics, Games Theory and so on. 
Maybe craft your own handbook based on what you learned from different lectures, books and write as many tips as you can when you are inside the subject. Then if you have to go back to your notes you will be way faster.

If you have this basis, what matters is to be able to take some perspective with your subject, and to be the most relevant is the hardest thing. 
Studying economics permits to shed lights on (not all) human behaviors, never forget that behind your proofs and lemmas !