Preheat oven to 350 degrees F.Melt the butter in a large skillet over medium heat.Add the chopped celery and onion into the skillet and cook until slightly soft, approximately 5 minutes.Empty the bag of the cornbread stuffing mix into a large bowl.Pour the vegetable mixture over cornbread mixture.Add the chicken broth and mix well. Add additional broth if necessary to get the necessary moistness.Add salt, pepper, sage, and poultry seasoning.Pour mixture into a baking pan and bake in a preheated oven until dressing is heated through, about 30 minutes.