Answer: The Tree of Souls
Quaritch detects that the Na'vi are accumulating their forces, and fears that they will soon have enough warriors to overwhelm the RDA base on Pandora. He knows that the Na'vi regard the Tree of Souls as their most important connection to their deity, Eywa, and he correctly concludes that the sacred tree would make an ideal target. In a speech to his troops that consists mostly of fear-mongering and manipulation, he convinces them that they should "strike at the heart of the Na'vi" by destroying the Tree of Souls. "We will fight terror with terror!" he proclaims.
Jake learns of the impending attack from Max Patel, a scientist from the RDA base, and starts mapping out his strategy to defend the Tree of Souls with Trudy and Norm. "We're going up against gunships with bows and arrows," Trudy observes, adding that she would prefer not to end up a martyr. Jake responds by saying that they have the advantage, as they are familiar with the terrain, and that the powerful flux vortex will wreak havoc with the RDA's instruments and guidance systems. When it is pointed out that the Na'vi will never recover if Quaritch succeeds in destroying their connection to Eywa, Jake's response is direct and to-the-point. "Well I guess we better stop him," he says.