Moroni saw the faithlessness of the Jaredites and saw that they did not accept the teachings of Ether. He claimed, “They did not believe, because they saw them not” (Ether 12:5). Then he added a caution to his readers, “Wherefore, dispute not because ye see not, for ye receive no witness until after the trial of your faith” (Ether 12:6).
In order to demonstrate the truth of this principle, Moroni drew upon a number of episodes in the Book of Mormon. He wrote, for instance, that it was by faith that “Alma and Amulek … caused the prison to tumble to the earth” (Ether 12:13). It was by faith that “Ammon and his brethren … wrought so great a miracle among the Lamanites” (v. 15). And it was because of the great faith of the brother of Jared that the Lord “could not withhold anything from his sight” (v. 21, see KnoWhy 246). Moroni adds, in verse 19, “And there were many whose faith was so exceedingly strong, even before Christ came, who could not be kept from within the veil, but truly saw with their eyes the things which they had beheld with an eye of faith, and they were glad.” Most of all, it was by faith and charity that these righteous individuals “obtained a promise” of those blessings that they most desired (12:17, 21, 22, 34, 37).
Book of Mormon Central, “Why Must a Trial of Faith Precede a Witness of Truth? (Ether 12:6),” KnoWhy 246 (December 6, 2016).
Book of Mormon Central, “How Can Trials of Faith Lead to Spiritual Growth? (Ether 12:6),” KnoWhy 356 (August 23, 2017). “Whatever their form, our mortal trials provide essential opportunities for spiritual growth.”