I always knew that the Book of Mormon was incredible and powerful. Here in these verses the Savior is going to teach us that the coming forth of the Book of Mormon will also serve as a sign to His people that the gathering of Israel is about to begin. The Book of Mormon however, isn't just a sign of the gathering, it is also the most powerful tool we have to assist in that gathering. God calls us to the work of the gathering. He is anxious for us to be a part. So no matter how you feel like you can join the cause, the important thing is that we join in in this great and marvelous work.