The Torah spends a couple of pages describing Avraham's desire to [be buried and] bury Sarah in a particular place - the Cave of the patriarchs. I find it difficult to comprehend this desire.
After one is dead and until the resurrection:
why the Cave was so important to Avraham and
what difference does it make where one is buried in general?
The Zohar Chodosh 97,2 says that Avraham scented Gan Eden at the entrance of Meoras Hamachpeila and desired to be buried there where Adam Harishon was buried.
רַבִּי קִיסְמָא אָמַר, מְעָרַת הַמַּכְפֵּלָה, סָמוּךְ לְפֶתַח גַּן עֵדֶן. בְּשָׁעָה שֶׁמֵּתָה חַוָּה, בָּא אָדָם לְקָבְרָהּ שָׁם. וְשָׁם הֵרִיחַ, מֵרֵיחוֹת גַּן עֵדֶן, בְּאוֹתוֹ הָרֵיחַ שֶׁהָיָה שָׁם. רָצָה לַחְצוֹב יוֹתֵר, יָצְתָה בַּת קוֹל וְאָמְרָה דַּיֶּיךָֹּ. בְּאוֹתָהּ שָׁעָה עָמַד, וְלֹא חָצַב יוֹתֵר, וְשָׁם נִקְבַּר. מִי נִתְעַסֵּק בּוֹ. שֵׁת בְּנוֹ, שֶׁהוּא הָיָה בִּדְמוּתוֹ וּבְצַלְמוֹ.
Rabbi Kisma said Meoras Hamachpeila was at the entrance to Gan Eiden. When Chava died, Adam went to bury her there. The aroma of Gan Eden wafted towards Adam. He wanted to make the cave larger and a Heavenly voice said "enough". Adam was buried by Seth his son there.
אָמַר רַבִּי רְחוּמָאי, הַקָּדוֹשׁ בָּרוּךְ הוּא נִתְעַסֵּק בּוֹ כְּשֶׁנּוֹצָר, וְנִתְעַסֵּק בּוֹ כְּשֶׁמֵּת. וְלֹא הָיָה מִי שֶׁיּוֹדֵעַ בּוֹ, עַד שֶׁבָּא אַבְרָהָם אַבְרָהָם אָבִינוּ עָלָיו הֲשָׁלוֹם, וְנִכְנַס לְשָׁם, וְרָאָה אוֹתוֹ, וְהֵרִיחַ רֵיחַ בְּשָׂמִים שֶׁל גַּן עֵדֶן, וְשָׁמַע קוֹל מַלְאֲכֵי הַשָּׁרֵת אוֹמְרִים, אָדָם הָרִאשׁוֹן קָבוּר שָׁם, וְאַבְרָהָם יִצְחָק וְיַעֲקֹב מוּכָנִים יִהְיוּ לַמָּקוֹם הַזֶּה. רָאָה הַנֵּר דּוֹלֵק, וְיָצָא. מִיָּד הָיְתָה תַּאֲוָותוֹ עַל הַמָּקוֹם הַזֶּה.
Rav Rechumi argued that G-d himself buried Adam so no-one knew of the existence of the entrance until Abraham entered there, saw and smelt the aroma from Gan Eiden. The Angel said Adam is buried here and Abraham Isaac and Jacob will be Buried here. Abraham desired to be buried there.
אָמַר רַב הוּנָא, קוֹדֶם שֶׁבָּא אַבְרָהָם, רַבִּים הָיוּ מְבַקְּשִׁים לִיקָּבֵר שָׁם, וּמַלְאֲכֵי הַשָּׁרֵת הָיוּ שׁוֹמְרִים הַמָּקוֹם, וְרוֹאִים אֵשׁ דּוֹלֶקֶת שָׁם, וְלֹא יָכְלוּ לִכְנוֹס, עַד שֶׁבָּא אַבְרָהָם וְנִכְנַס, וְקָנָה אֶת הַמָּקוֹם.
Rav Huna said until Abraham came many that wanted to be buried there but the angels guarded the cave from them, they saw a fire and couldn't get in. Until Avraham managed to enter in his greatness, he bought the Cave to be buried there.
3 And Abraham arose from before his dead, and he spoke to the sons of Heth, saying
4 "I am a stranger and an inhabitant with you. Give me burial property with you, so that I may bury my dead from before me."
RASHI
I am a stranger and an inhabitant with you: [I am] a stranger from another land, and I have settled among you. [Consequently, I have no ancestral burial plot here (Rashbam, Sforno).] And the Midrash Aggadah (Gen. Rabbah 58:6) [states]: If you are willing [to sell me burial property], I am a stranger, but if not, I will be as an inhabitant and will take it legally, for the Holy One, blessed be He, said to me, “To your seed I will give this land” (above 12:7).
Rav Hirsch points out on verse 3 the source for the law of onein:
he only left his dead to make arrangements for it; hence our sages lay down the law that as long as the dead be unburied; the relative is to think of nothing else than attending to the business of seeing that the dead receives its due. Until the burial is duly carried out, this, and nothing else at all, is to receive all his attention.
Rav Hirsch continues on verse 4:
Abraham does not ask for permission just to bury his wife. He wants his wife to rest in her permanent everlasting possession of her resting-place, that is why he first asks for the right to acquire a piece of land as freehold property for the purpose of a sephulcre.
Rav Hirsch continues on verse 19 that this particular location is requested because it was also the burial place of Adam and Eve, the progenitures of all mankind and, therefore, had a particular holiness. The cave (Machpelah - doubled) had locations for pairs to be buried so that he would be buried with Sarah. There were other pairs so that Yitzchak and his future wife and the heir of Yitzchak and his future wife could also be buried there.
Therein lies the thought that the particular place where it was wished that the burial was to be made had special value for the one who was to be buried there, or for those who belonged to him. It says that he is not just to be buried, but to be buried there. Now tradition says that Sarah was not the first to be buried in that cave. Adam and Eve already rested there. The parents of mankind were the first and they are to be joined by the parents of the Jewish people, those spiritual parents of mankind, that was why Abraham chose just this cave.
Malbim (footnote to 23:20) explains that Avraham wanted to demonstrate to the Bnei Ches the truths of the soul's continued existence and its eventual resurrection. (That requires, then, that the deceased be buried with their own family and with people of their caliber - אין קוברים רשע אצל צדיק. If that weren't the case, there'd be nothing wrong with a temporary burial just to get the dead body out of the way, and then eventually disinterring it.)
That he wanted specifically the Me'aras Hamachpeilah, the Malbim goes on to explain, is because its structure - בית ועליה על גביו - represents the human being in this lower world, with Olam Haba above it.
