The wedding massacre reiterates how greatly honor is valued in Westeros, and what lengths some will go to in order to get revenge. The act that precipitated the massacre is Robb’s deciding to marry Jeyne Westerling and not one of the Frey girls, as he had promised. Robb and Catelyn knew immediately that Walder Frey, the patriarch of the Frey family, would not take the news well. Walder is notoriously sensitive to slights, and he would perceive the move as a serious affront to his family’s honor. Robb thought the outcome might be that he would lose the Frey’s support in his cause, but in this episode it becomes clear that Walder Frey took the insult much more seriously than anyone had anticipated. Walder evidently struck up an alliance with the Lannisters and planned to murder Robb, Catelyn, and the others at his own daughter’s wedding. (The Lannisters’ involvement is suggested by the playing of The Rains of Castamere, a song about Tywin Lannisters’s destroying a family that crossed him, and Robb’s killer saying “Jaime Lannister sends his regards.) According to the customs of Westeros, it’s forbidden to harm a guest in your house. Doing so is a major breach of honor, so Walder basically sacrifices his and his family’s honor for the sake of revenge, all because of a slight to his honor.