In Bereishit 32:22 the Torah states, ויבוא אברהם לספוד לשרה ולבכותה, Avraham came to mourn for Sarah and to weep for her. There are two approaches one can take to understanding this Pasuk. One can say that Avraham was mourning his personal loss, for he would now have to live the rest of his life without his עזר כנגדו. Or, one can say that he was mourning the world's loss, since everyone would now miss her righteous presence. In 32:3-4 the Torah states, וידבר אל בני חת לאמר. The word לאמר is normally used in the sense of telling something over to future generations. For example, in Shemot, וידבר ה' אל משה לאמר means that the following words in the text are crucial for the Mesorah to properly be passed on. Here, Avraham wanted to show what an important effect Sarah had on him as well as on all the people around her. Since she accomplished so much and affected so many people, she deserved to be buried in a place of respect - a cave which will never be touched. Because a cave, unlike a field, can't be used for farming, this burial site could be preserved for generations.
We thus learn a very important lesson. We see how Avraham treated Sarah with the utmost respect because of how she affected others, and because of how she affected him. We must learn this lesson and always treat people with respect, treating them the way we would want them to treat us.