Julia Child wrote her cookbook in English, and that is why we can understand and follow her directions. If the cookbook had been in French, at least some of us would have a hard time understanding what to do.
To program a computer we must first agree on a language that both we, as programmers, and the computer understand. A computer is not sophisticated enough to understand a natural language like English or French, so we must settle on one of many possible computer languages.
A computer is also not intelligent enough to make inferences about what we mean if we don't use the proper grammer. A native English speaker can easily understand the meaning of this sentence "I ain't gonna go nowhere, nohow, not never." However, when we communicate with the computer in the computer's language, we must use the proper grammar at all times. If we speak improperly, the computer will simply inform us of our error and give up.