As far as sanctification is concerned, those souls which are free of the body have an advantage over those still living in the flesh. It is true that they receive, through the prayers of the priest and the intercession of the holy offerings, purification and remission of their sin, and do not add new wrongdoing to the old, as most of the living do; they are either entirely absolved from all blame, or at least freed forever from the possibility of further sin. Because of this, they are better disposed for communion with the Savior, not only than the majority of the living, but also than they themselves would have been if they were still in the flesh. The very fact of being free from the bonds of the flesh makes them far more worthy to receive the holy Mysteries than they could possible have been if they were still housed in their bodies.
We know that in the next world there are many mansions, so that every degree of goodness may be glorified, and none may go unrewarded by the most just and loving Judge. Thus, those worthy of the greatest rewards, who are perfect, and who inherit perfect blessedness, such as St. Paul, enjoy this happiness more purely after death than they did while still in this life. So also those who are called to a lower position in this place of rest naturally gain more fruit from the Mysteries than they did while they were alive.
We have shown that all peace of soul and the entire reward of virtue, be it great or small, consists only in this Bread and this Chalice, which is partaken of by both the living and the dead. That is why our Lord Himself describes the future happiness of the Saints as a banquet; it is in order to show that in the next life there will be nothing save the Holy Table. Thus, the holy sacrifice of the Eucharist is for the dead as well as the living, and just as the latter, as we have said, receive a two-fold sanctification, so do the former. The dead are in no way inferior to the living; rather, they possess certain advantages over them. (A Commentary on the Divine Liturgy, 45: A Theological Parenthesis)