Despite Harry’s ever-growing distrust of Snape, which is only accentuated by his discovery that it was Snape who leaked the prophecy to Voldemort, Dumbledore still continues to believe that Snape is loyal to the Order. Harry simply cannot understand how Dumbledore can completely ignore all the evidence that points to Snape’s inherent evilness. It hurts Harry to think that Dumbledore is being taken advantage of by Snape, and he begins to wonder if Dumbledore is growing too old and too out of touch to truly protect Hogwarts and help Harry stop Voldemort. Harry’s skepticism is natural, but Dumbledore has certainly earned Harry’s trust, and Harry can do nothing but accept that Dumbledore has good reason to believe that Snape is not betraying the Order. All of this does little to calm Harry’s nerves, however. Like his father and godfather, Harry believes that Snape is entirely untrustworthy. Once again, Dumbledore promises Harry that Hogwarts will be protected in their absence and seems strangely unconcerned that Draco was caught whooping with excitement in the Room of Requirement. Clearly, Dumbledore knows more about what goes on at his school than he lets on.
Throughout the series, Rowling has never given us reason to think that Dumbledore is anything other than a wise and powerful wizard. Accordingly, it seems highly unlikely that Dumbledore would be so incredibly nonchalant about Snape and Draco were he not in some way already clued in to their plans. Harry is bewildered by Dumbledore’s behavior, but since we can infer that Dumbledore knows things he is not telling Harry, we get a sense of foreshadowing that events will turn out in a way that will surprise Harry. Before Dumbledore and Harry leave for the cave, Dumbledore insists that Harry give his word that he will follow any and all of Dumbledore’s orders. Again, Rowling is foreshadowing events to come. Harry reluctantly promises to do whatever Dumbledore tells him to, no matter how unpleasant or disappointing, and we begin to suspect that their journey may be more tumultuous than expected—and that Dumbledore, once again, knows exactly what lies ahead.