The "death foretold" that this novel refers to is that of Santiago Nasar, a young man about town who was murdered after being falsely accused of "raping" bride-to-be Angela Vicario, and thus taking away her virginity. In a shameless game of social double standards, Angela is beaten and sent back to her family upon her husband's discovery of her non-virginity. Santiago's killing by the Vicario twins represents a barbaric way of avenging the alleged honor that Santiago's actions took away from Angela and her family. It also avenges the Vicario name, which was stained by the discovery as well.
"We killed him openly," Pedro Vicario said, "but we're innocent." "Perhaps before God," said Father Amador. "Before God and before men," Pablo Vicario said. "It was a matter of honor.
And what exactly is this "honor"?
To the modern reader, the murder of Santiago may appear vicious and nonsensical. However, within the historical context where the novel takes place (a small town within the Caribbean region of Colombia, South America), a family name and your reputation was all to be had as a way to establish the value and worthiness--the honor--of your clan. This male-dominated society had strict expectations for women, with "virginity" symbolizing a woman's highest honor.
Even when it was less than two months before she would be married, Pura Vicario wouldn't let her go out alone with Bayardo San Roman to see the house where they were going to live, but she and the blind father accompanied her to watch over her honor.
Honor is everything in this community. It represents an opportunity to offer "good women" as means of networking among families, to make good marriages and expand riches. For women, honor is represented in the form of a universally-preserved virginal status. Honor for men is embodied in a good name that one does anything to defend.
It also represents that the women are "well-bred" and come from honorable families in which "good mothers" and watchful fathers dominate the household with staunch, regimental rules.
Essentially, what Angela Vicario did was play the system and its antiquated and broken honor code by falsely blaming a man who would inevitably be killed by those who felt offended by him. In turn, she would have a good scapegoat to blame after being publicly shamed by the family that she was going to marry into, and find an even better excuse to make up for the debacle that her actions caused.
Hence, this dishonorable way to defend an honor that was not even there in the first place makes the novel all the more ironical, making the reader question if, in the end, this concept of "honor" is actually a giant diminished, a thinly-veiled creation behind which people hide to attempt to appear "civilized."