How to use "fearful" in a sentence

Before entering upon so grave a matter as the destruction of our national fabric, with all its benefits, its memories, and its hopes, would it not be wise to ascertain precisely why we do it? Will you hazard so desperate a step while there is any possibility that any portion of the ills you fly from have no real existence? Will you, while the certain ills you fly to are greater than all the real ones you fly from - will you risk the commission of so fearful a mistake?