In Candide, chapter 30, work keeps Candide, Pangloss, Martin, and Cacambo from what three great evils?

In the final chapter of Candide, Candide, Pangloss, Martin, Cacambo, Cunegonde, and the old woman settle down and decide to "cultivate the garden." The Turk whom they speak to in this chapter tells them the following:

“You must have a vast and magnificent estate,” said Candide to the Turk.
“I have only twenty acres,” replied the old man; “I and my children cultivate them; our labour preserves us from three great evils—weariness, vice, and want.” (Chapter 30)

Here, the Turk says that his family's "labour," or work, protects them from "weariness, vice, and want." In other words, their work keeps them from being world-weary or hopeless, stops them from committing immoral acts, and makes them feel satisfied enough that they do not "want" for anything more. The act of work—in Candide and his friends' case, tending to the garden—keeps people occupied and out of trouble.
Work is here presented as an alternative to philosophizing, which is what our characters have been doing for most of the novel. Pangloss continues to try to prove his flawed optimistic theory in the final chapter of the novel, but Candide seems to have moved past it, just wanting to work in the garden. The characters experienced and witnessed the most extreme events imaginable in their journeys around Europe and South America. It makes sense that they now want to settle into a calmer and more stable life. The ending can also be read as one of resignation; after not being able to find the best world that Pangloss taught him about, Candide sort of gives up and lives a simple life instead.