Whoever reads it will understand. In the following vision, St. John, Apostle and Evangelist, witnessed the assumption of the Blessed Virgin Mary, body and soul, into Heaven. St. John must have recounted what he saw to St. Peter the Chief Apostle and other Apostles. This revelation to St. John became part of Sacred Tradition of the Church. When Pope Pius XII declared the Dogma on the Assumption of Our Lady in 1955, he only affirmed what the Catholic Church has believed for the last 2,000 years.
Nothing is new.
In fact, all the Dogmas of the Catholic Church are based on public divine revelations which ended with the Apostles of Our Lord. It is difficult to ascertain it. If one judges by the flowers that form a crown around the dead body, one should say that only a few hours have gone by. But if one judges by the olive branches on which the fresh flowers are lying, branches with leaves already withered, and by the other withered flowers lying like relics on the cover of the chest, one must conclude that some days have by now gone by. But Mary's body is exactly the same as it was when She breath Her last.