In the story, Adam says his dad's speech was as good as anything the preacher had ever done on "hell-fire and damnation." This refers to the kind of church sermon where a preacher would try to motivate his congregation by threatening them that they were going to hell. This sort of sermon was supposed to appeal to people's emotions to get them to act in a certain way. Adam's dad's speech does that.
He feels his father is as good of a speaker because of the effect of the speech -- it gets the people all fired up and helps make them decide to fight the British.