Ed is appropriately cautious and, armed with his gadgetry for detecting the paranormal, committed to his craft. Lorraine is a clairvoyant who employs her sixth sense with self-emptying compassion. When this duo arrives at the farmhouse, they provoke the sinister forces haunting the Perron family and the surrounding acreage in an all-hell-breaks-loose sort of way. They're like walking icons.
The Conjuring's prologue is a touch confusing and could use better-edited transitions, but the opening scenes still smartly frame the main story in a couple of ways. First, it establishes Ed and Lorraine Warren as the heart—the center—of the film. Before we're introduced to the Perrons, we know that investigative relief is in reserve.
Second, playing up its based-on-a-true-story self-awareness, the film's prologue ends by suggesting that one case in particular in "the Warren files" is so "malevolent" that they've been reticent to share the details about the case "until now." And the "until now" is made emphatic when the title screen subsequently appears in large, throwback type, a touch that induces 70's/80's horror nostalgia. Ironically, nostalgia lets the viewer feel at home—just as Wan transitions into the Perrons' moving into the most inhospitable farmhouse.
This "true story" realism that suggests "you're about to witness one of the ugliest recorded happenings"—coupled with the sense of respite that the Warrens provide—sets the tempo for the film's pace and tension.
Shortly after the Warrens arrive to help, and we've been spooked a few times, Carolyn Perron says, "I think the kids feel a lot safer with you around." And "the kids" includes this viewer, at least, because I could feel the calming effect of Warrens' presence before Mrs. Perron gave voice to it.
That's no small achievement: the Warrens are genuinely likable and trustworthy. Together, they offer a welcoming presence that's a functional resistance against the demonic presence haunting the house and land. This horror film isn't content to merely batter you into submission, but offers a genuinely scary thriller that's able to hit the right beats to be both appropriately horrifying and enjoyable. The Warrens form a hopeful through line from beginning to end.
Incorporating plenty of references to previous horror classics, Wan utilizes nearly every genre convention on offer—including demon possession, witchcraft, clairvoyance, paranormal investigation, creepy dolls, and more—but he gives all of these time-honored scares enough space to coherently frighten by setting the film in a place that can house all of these horrors.