In life, things are categorized into two groups; Need and Want. There are things we need and things we want.
We decide on the importance of such things in our lives based on whether it satisfies our needs or our wants.
We can go through life with out things we want; however, we cannot live without the things we need, therefore, if the need arises and nobody can satisfy that need, we are motivated to create the things we need to live.
There are also things we want so much that it becomes a need. Thus, we are motivated to create a version of the thing we want to satisfy that need. For example, even though we already have a lot of jeans, we want to buy a new pair of jeans but we can't afford such expensive item. So, we find ways to create our own version of the expensive jeans from the items we have on hand. The end product will satisfy our need of acquiring the things we want.
Well that would be sight; to create clear images of the forest and the hills.
I know that because the author is describing everything. Hope this helps!
It is necessary because if you don't have a confirmed opinion with textual evidence to back it up you wont have a good argument.
