Why you should do flashcards / spaced repetition
not to memorize just to memorize, but memorize so that when you see stuff, you can RECOGNIZE and UNDERSTAND it in context - which has a way bigger effect for learning
also good to memorize the first 1000-2000 concepts such that you have a bit of a cognitive scaffolding to understand context and slot any new things into. This also helps in training intuition.
This is true not just for words and language but also for coding languages or mathematical formulae or chemical formulae.