To show that their souls are alive, and have not passed into non-existence as the irrational beasts.
In confirmation of the General Resurrection.
In confirmation of the Last Judgment.
To confirm that each of them has not yet received his reward (as the Holy Fathers teach).
To remind us that they are our members, and that we ought to commemorate them.
To help them. ‘For sacrifices and almsgiving help some, effecting for them a complete remission; while for those who have been condemned, they perhaps make the punishment more tolerable’ (St. Augustine, Enchiridion, Chap. 110)
To comfort and console their relatives who are still alive.
In accordance with teaching of the greatest antiquity, handed down to us from the Fathers, that we should pray for those who have fallen asleep to commemorate them.
Because we are under obligation to pray for one another. The Calvinolutherans are thus misanthropists and haters of their brethren, for after burying their kinfolk they then refuse to make any further mention of them. (Eustratios Argenti, A Study of the Greek Church Under Turkish Rule by Kallistos Ware, pp. 157-158)