How to learn a great number of theorems by heart? Imagine you have ten definitions and you want to learn them by heart. It is easy - definitions are somehow unique. But, imagine 40 (60,100,1000) theorems that all look somehow similar and are all important. How would you learn them by heart? What the word "learn" mean here for you?
Of course, you can learn them by numbers, and everytime I will say "Theorem 147" you will say the right one. But somehow it is not right. We do not call people with their birth date, do we?
If so, how would you categorize the (limited number of) theorems? What would be your approach to learn tens of theorems by heart and still clearly distinguish between them? What makes a theorem unique? Could you draw a graph or a tree of theorems? 

There is really no point in memorizing $1000$ theorems.  For one thing, different expositions of the same subject will organize the theorems somewhat 
differently.  A particular theorem in textbook A might correspond to parts of several different theorems in textbook B, or might just be an exercise in textbook C.
