There’s no question. None at all. Fluency in any language comes from what we read and what we hear. This is what the research tells us. And this is what the experience of many language learners tells us.
The most important principal of language acquisition is very simple: we acquire, or pick up, language when we read or hear interesting and comprehensible, or understandable, input. Now there’s a new word that helps us choose what to read or listen to.