The Power of Language in Building Intersubjectivity

In the book, you say that grammar carries a huge functional load in building intersubjectivity by increase in common ground. Can you just walk me through that sentence? Because I feel like it's super important. What we're doing there is simply acknowledging and pointing out something really basic that linguists have pointed out about language itself. Languages allow you to productively take small bits of conventionalized meaning and say completely novel, unique things.