In the Byzantine part of the Church, theologians and preachers had been reflecting on Mary's relationship to Jesus the Highpriest. They realised that Mary had to be priestly herself since she gave birth to the Priest of Priests.

A legend grew up that stated that Mary had spent her youth in the Holy of Holies of the temple of Jerusalem.

“There where only the High Priest may enter, and then rarely - only once a year, it is there in this holy sanctuary of grace that Mary is offered to stay there indefinitely. Who has ever heard anything similar? Who has ever seen or heard, now or formerly, that a woman was introduced into the intimacy of the Holy of Holies, and that it was in this place, almost inaccessible even to men, that she lived and ate. Is this not a striking demonstration of the strange magnificence of which her womb would be the object? Is it not a manifest sign, a irrefutable proof?” - St Germanus 633 - 733

The Greek Fathers expressed their belief in Mary's priestly status in the many new titles which they gave her. St Andrew of Crete mentions the following:
* ‘spiritual altar of the divine victim, altar consecrated and dedicated to God’;
* 'priestly staff';
* ‘sanctuary of all sacrificial worship’;
* 'the most holy table [= altar] which has carried by itself the living bread, Our Lord and God Jesus Christ, eternal life made bread . . . . ’.

from an ancient fresco