Here is a direct quote from Susan Gross during one of her sessions at NTPRS. You really can't make it any more simple than this:
Grammar clarifies meaning. That is its role in language.
Then Susie gave the following example:
a dansé =
By the time each batch of bricks is labeled and "understood" by the class (as evidenced by the bogus test), as in the case of the relative pronouns brick which takes over a week or ten days to look at, and
Now that my vision is finally clear about this topic of grammar acquisition, I can see that, when the kids translate a reading text and, in doing so, get the image of a movie in their heads, they are learning
Showing the kids how the relative pronoun bricks and all those other bricks fit together is a waste of time. It's all done in English. It's like making the kids do a picture puzzle. So few even want to complete
In the past century, teachers would take a batch of bricks, grammar points arranged in chapters in books, and, laboriously, each day, boldly, inflict a kind of analytical pain session on the kids about the nature of that particular brick.