While abridging the prophet Ether’s words on faith, Moroni included some of his own testimony, counsel, and understanding about the subject.
And now, I, Moroni, would speak somewhat concerning these things; I would show unto the world that faith is things which are hoped for and not seen; wherefore, dispute not because ye see not, for ye receive no witness until after the trial of your faith
A trial of faith precedes a witness of truth. A trial of faith is essential to a testimony of the gospel of Jesus Christ. Let us therefore continue in faith, knowing that a testimony will come or that your testimony will increase as you exercise your faith.
Source: Ether 12:6; The Book of Mormon: Another Testament of Jesus Christ