Since it is impossible to know all these persons, whose number is uncountable, the Catholic Church cannot properly worship each one of these Saints by offering them a formal homage as she does with the canonized Saints. So, she instituted the feast of All Saints, a day on which she venerates them all.
It is the veneration of all souls that are in Heaven, even if they are not officially canonized or beatified. Anyone who is in Heaven is a holy person. He or she is in the presence of God, sees God face-to-face, and is entirely pleasing to God.