expression
you can't do something if you don't know how to do it
Proverb meaning that without learning or practice, one cannot perform a task. The literal meaning is 'you can't read a sutra you haven't learned'.
習わぬ経は読めぬというから、まずは基本をしっかり学ぼう。
As the saying goes, you can't read a sutra you haven't learned, so let's first learn the basics thoroughly.