The curtain of the Royal Door is half-closed – as opposed to being fully closed during other Liturgies – during the Liturgy of Presanctified Gifts immediately after Now the Powers, which corresponds to the Cherubic Hymn in other Liturgies and during the singing of which the Holy Gifts are transferred from the Oblation Table to the Holy Table. This is explained by the fact that the Liturgy of the Presanctified is not a full-rite Liturgy.
According to Hermogen Shimansky, a prominent Russian liturgical scholar, it signifies that the Holy Sacrament of Eucharist has already taken place, and the celebration of the said Sacrament has already been demonstrated to us but it still remains inscrutable for us, like the very mystery of our redemption by the suffering and death of our Lord Jesus Christ. The fact that the curtain is half-closed additionally points at the incompleteness of the Liturgy of Presanctified Gifts.
Nevertheless, referring to this Liturgy as incomplete does not by any means point at its inferiority and does not mean that it is less important. The focus of every Liturgy is the communion of the Body and the Blood of Christ, through which a human being, according to the holy fathers, receives the ‘yeast of immortality’ and becomes a participant of eternal life.
Translated by The Catalog of Good Deeds