It's pretty obvious. He's about to murder the family. He is the monster. The monster is the hatred that's been festering in him, he's personified it. What he's "staring at" in the distance is the monster. i.e. He's envisioning it. Notice every time the monster is mentioned it's accompanied by the man staring, or watching, etc? Until the end, when he and the monster are both reaching to open the door... they have found synchronicity.
It's pretty obvious. He's about to murder the family. He is the monster. The monster is the hatred that's been festering in him, he's personified it. What he's "staring at" in the distance is the monster. i.e. He's envisioning it. Notice every time the monster is mentioned it's accompanied by the man staring, or watching, etc? Until the end, when he and the monster are both reaching to open the door... they have found synchronicity.