Here is a succinct summary of the value of input from a letter that Stephen Krashen submitted to Newsweek.
I agree with him. Of course it is great to speak, when you have enough words, when you have the opportunity. However, listening and reading are easy to arrange and control, especially today. And you need to understand before you can speak.
“The more you listen and read, the better off you are.Prof. Gollan’s remark about languages, “The more you use it, the
better off you are” is nearly correct (“Why it’s smart to be
bilingual,” August 7) Our research over the last four decades shows
that it is input that counts: We acquire language when we understand
what we hear and read. This means that the more you listen and read,
the better off you are. It also means that it doesn’t help to talk to
the mirror or read out-loud from books. But real conversation, when
other people talk to you, and reading books you find interesting will
help a lot. Stephen Krashen”