Moroni gave his own endorsement of Isaiah’s writings, just as other Book of Mormon prophets had. This endorsement was intended for those of us who live in the latter days. He also testified that those Saints who have lived in the New World but passed on continue to pray and exercise faith that God will remember his covenant with those still living. Righteous people on the other side of the veil act in faith just as we do. Various individuals have been shown the activities of Saints in the spirit world and have seen that the departed offer prayers for the living and exercise faith in their behalf. The journal of Sister Janet Skinner’s grandmother recorded her struggle over the death of a teenage daughter many years before. On one occasion, stricken with grief, the grandmother opened her eyes to a vision of the spirit world. She wrote: “I saw three personages clothed in white, two kneeling and one standing [in] back of them. They had their hands folded in the attitude of prayer. I knew they were praying for me. This was the first time I knew that loved ones on the other side could pray for us here.”
Compare the statement from President Joseph F. Smith in “Angels Are Coming to Visit the Earth,” in the commentary at 1 Nephi 3:29–30.