Babies are often observed of having amazing linguistic ability. It's sheer because of their repetition ability. Russell wrote about his daughter: At the age of eighteen months, when supposed to be sleeping, she was overhead saying to herself: "Last year I used to dive off the diving-board, I did."

Obviously, the whole sentence doesn't mean anything to her.

When we are learning as an adult, we still need this stage. The more important is the next stage: put known words and structures into a sentence which carries the meaning you intend it to. That requires a lot of power and manipulation.