Vatamot Sarah beKiryat-arba - Sarah died in Kiryat-arba

Peshat

The main thrust of the verse is to alert us to the fact that this righteous woman died and was buried in Eretz Yisrael.  The Torah emphasizes that the place called Kiryat-arba at that time was renamed Chevron afterwards in order that no one should forget that we speak about a town inside Eretz Yisrael 

At the conclusion of Sarah's burial in v19, the Torah repeats once more that the Cave of Machpelah where she is buried is situated "at Chevron in the land of Kenaan."  The Torah teaches that it was a great privilege to be buried in the same burial ground reserved for such outstanding individuals as Adam, Avraham, Yitzchak, and Yaakov.

Drash

The reason the town was called Kiryat-arba (the city of Four), is because four pairs of outstanding human beings were buried in the Cave of Machpelah there. 

They are: Adam and Chavah, Avraham and Sarah, Yitzchak and Rivkah, and Yaakov and Leah.

Sod

The mystical dimension of the name Chevron is that the soul of everyone buried in that cave joins the mitchaber, the celestial city of G-d, i.e. the four encampments of the Shekinah.  Our patriarchs would not have made great efforts to be buried there had they not been aware of a profound spiritual dimension involved.  They knew that transfer to the Olam haEmet  (the World of Truth) from that site would be a crucial experience for them.  It is the place from which the souls return to their origin, the Throne of G-d's glory.