The Talmud, in Maseches Kiddushin (2a), compares the acquisition of a burial plot for Sarah to the halachic method of marriage. Just as land is purchased with money, so too, one method of marrying someone involves the giving of money or an object of value from a man to a woman. What is the meaning of this comparison? How can the purchase of a burial plot be the model for the marriage ceremony?
The most important character trait necessary for a successful marriage is chessed. Most of Parshas Chayei Sarah focuses on Eliezer's search for a wife for Yitzchak. It is Rivka's excellent performance of chessed that qualifies her as one fitting to marry Yitzchak.
Chessed can be performed for two reasons. Some give to others with the hope that they will receive something in return. A higher form of chessed involves giving without any ulterior motive, without hope of receiving something in return. We are required to perform acts of chessed, in emulation of Hashem's ways. Just as He visits the sick, feeds the poor, and cares for everyone's needs, so too are we commanded to follow His path. Hashem's acts of chessed constitute the higher form because there is no way for us to return such acts.
Chazal refer to the prototype of chessed with absolutely no ulterior motive as "chessed shel emes"- true loving kindness - the ultimate act of which is caring for the dead. It is this model of chessed that is portrayed by the purchase of a burial plot for Sarah as Avraham had nothing to gain in return. It is this chessed shel emes that serves as the model for eternity for the chessed done between husband and wife. Partners in marriage may tend to be kind to each other because they will receive kindness in return. The Torah stresses that the correct mindset for caring for ones spouse is to give for the sake of giving, not for the sake of receiving. At the beginning of every Jewish marriage, as the kiddushin are performed, the image of Avraham caring for Sarah is conjured up.
Parshas Chayei Sarah is truly the parsha that teaches us the secret of marriage. Avraham and Rivka's acts of chessed guide us through marriage as we perfect ourselves as givers in the true sense of the word.