Because the brother of Jared knew there was a God, because he had a correct idea of the character, perfections, and attributes of God, and because he was willing to sacrifice anything to better know and serve that God, he gained the assurance that his course in life was pleasing to the heavens (see Lectures on Faith 3:2-5).
He acquired the quality and kind of faith which brings remission of sins, assures the redemption of souls from death and hell and endless torment, and eventually brings them into the presence of God. His faith was made perfect in and through Christ. It is not simply that the brother of Jared had intellectual understanding about divine things. He was not merely a bright theologian. Rather, he was a participant in the religion of Jesus Christ, that religion which enlightens the mind and sanctifies the soul