I agree with Peachey about the importance of interaction.
In my case it is because of my memory i helped by a strong emotional activation during interaction.
I give you an example from my experience: in the first audio chat with a new language partner, it happens to fall in some misunderstanding, just because i despertely need to espress an idea but I can't find the right word in my brain.
And when I succeed to find the right word (even if it's suggested by the partner) something appens in my emotional field.
And in some way, this word appears to me lika a savior.
Because I was desiring, like water in the desert.
That word begins to live with a strong energy in my memory.
I agree with Fuad...for understanding the importance of listening in learning second language, just imaging all the babies, all around the world! How do they learn to speak?! This is how human brain works, and is a established scientific fact in psychological studies...