If you don't want to know the circumstances surrounding Monday's entry in this slideshow, then don't read any further...
[spoiler]Monday's quote:
Ep #1156 (1840) - Samantha - 'Yes, I MUST, MUSTN'T I? I never really believed that Quentin's interest in the black arts was anything but a foolish eccentricity-- but I MUST now-- I do!'
From "#1154_1155/1156: Robservations 11/05/03: A Death; An Arrest For Murder"
Collinwood - Samantha looks out the window. Trask enters--I don't think I should leave until the constable makes his decision, he says. Where is the constable now? asks Samantha. He just left Gabriel and has gone up to see Quentin, says Trask. What am I going to do when he comes down? she asks. Whatever your conscience dictates, my dear, says Trask. My son...says Samantha. Trask reminds her, it would be worse for him to grow up in this atmosphere of evil--when I think of the heinous practices that have gone on in this house! Please, Lamar, she begs. Painful as it is, says Trask, you must protect your son from his own father. I must, she agrees, I never really believed Quentin's interest in the black arts was anything more than a foolish eccentricity, but I must now--I do! You have just made the most important choice of your life, says Lamar--you have crossed the river of indecision and joined those on the other side that would be saved! Sam smiles proudly.
[/spoiler]
The Robservations references the quote quite well, though out of context the quote is deceiving because it appears that the first part is also about Samantha's conclusion that Quentin's interest in the black arts is more than a foolish eccentricity. However, as the Robservations excerpt shows, in context it's actually about protecting Tad.