Today the Church commemorates all of those who "have gone before us with the sign of peace and are now at rest." This feast was, in the Latin Church, begun with the consecration of the Pantheon in Rome to St. Mary and all Martyrs. Later, in the middle ages, it was moved to November 1.
The readings for today's Mass remind us that "what we will be then," i.e., in heaven, has not yet been revealed to us. We are on our way, becoming what we shall be on that day. They remind us also of that vast throng "which no man could number, of every tribe, language, people and nation," who are washed in the blood of the Lamb (Holy Baptism) and wearing white robes, with palm branches in their hands, give eternal worship with all the angels to the All-holy, and Blessed Trinity of Father, Son, and Holy Ghost, one God, for ever and ever.