Place the bacon in a saute pan over medium-high heat and saute until bacon is crisp. Add the celery, onions, and carrots and cook until the vegetables are translucent, about 5 minutes. Add the lentils and the bay leaves and cook for 1 minute. Add the chicken stock and bring to a boil. Lower the heat to a simmer, cover, and cook for 20 to 30 minutes, until the lentils are tender. Season with salt and pepper.