Compare the words of Moroni when discussing the brother of Jared's marvelous vision on Mount Shelem:
15 Behold, when ye shall rend that veil of unbelief which doth cause you to remain in your awful state of wickedness, and hardness of heart, and blindness of mind, then shall the great and marvelous things which have been hid up from the foundation of the world from you—yea, when ye shall call upon the Father in my name, with a broken heart and a contrite spirit, then shall ye know that the Father hath remembered the covenant which he made unto your fathers, O house of Israel. (Ether 4)
...with these words from Alma-2:
9 And now Alma began to expound these things unto him, saying: It is given unto many to know the mysteries of God; nevertheless they are laid under a strict command that they shall not impart only according to the portion of his word which he doth grant unto the children of men, according to the heed and diligence which they give unto him.
10 And therefore, he that will harden his heart, the same receiveth the lesser portion of the word; and he that will not harden his heart, to him is given the greater portion of the word, until it is given unto him to know the mysteries of God until he know them in full.
11 And they that will harden their hearts, to them is given the lesser portion of the word until they know nothing concerning his mysteries; and then they are taken captive by the devil, and led by his will down to destruction. Now this is what is meant by the chains of hell. (Alma 12)
Moroni references a "veil of unbelief," whereas Alma references the "chains of hell," and both equate this to having a hard heart. Notice that in the vision of Enoch, found in the Book of Moses, both of these visual metaphors are used together:
26 And he beheld Satan; and he had a great chain in his hand, and it veiled the whole face of the earth with darkness; and he looked up and laughed, and his angels rejoiced. (Moses 7)
One very clear and consistent theme in the Book of Mormon (and many other scriptures) is that our unbelief gives Satan great power over us. We "rend the veil of unbelief" when we exercise faith in God and give heed and diligence to his word.
