Importance of every word in the torah

There is this concept that every word in the torah has
importance to it and that it was written for a reason.

Having learned in Chumash that there is a kind of a repetitionof the ten commandments, before having learned this I want to ask you why you think there is that repetition, and how that concept can be applied to this. Some can argue that this shows that not every word in the torah is significant and some can be left out. Tell me what you think!