There was no obligation to reveal himself to this man, Matt had been faced with this question before. He also had given the information freely to a few, that strange woman from the island Leeloo and then his current girlfriend Rose Tyler. Both of them had been keen enough to see through his facade, but not as quickly as this guy. "I call it a Sonic Sense, it's sort of like echolocation...you know, the way a bat sees without really being able to see. I can hear things and they create a vision." He hoped that was explaination enough.
When confronted with a question of embracing this strange calling and harming the innocent, finally Matt began to get a bit irritated with the constant prodding, "I didn't pick this, it was chosen for me and what better than a Devil to instill fear into the heart of someone with ill intent?" Gritting his teeth, Matt narrowed his eyes, stung by an accusation made by the man, "I would never intentionally harm someone that's innocent. I protect them day and night. I'm a lawyer by trade, I serve the people that can't protect themselves from evil."