Brother of Jared's vision is found in Ether chapter 3 Below are some of my thoughts.
Moroni reiterates that the Brother of Jared could no longer be kept without the veil, becuase of his faith.
Ether12:21
21 And after the brother of Jared had beheld the finger of the Lord, because of the promise which the brother of Jared had obtained by faith, the Lord could not withhold anything from his sight; wherefore he showed him all things, for he could no longer be kept without the veil.
Moroni also mentions that there was many other people that could not be kept from the veil.
Ether 12:19
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.
How can we have this same experience? Answer: By exercising fatih and being sanctified in Christ.
Ether 4:7
7 And in that day that they shall exercise faith in me, saith the Lord, even as the brother of Jared did, that they may become sanctified in me, then will I manifest unto them the things which the brother of Jared saw, even to the unfolding unto them all my revelations, saith Jesus Christ, the Son of God, the Father of the heavens and of the earth, and all things that in them are.