When considering the posture of the priest in the Eucharist it occurs to me that he must be seen in the context of the other symbols of Christ within the space. The following reflection is not rigorously academic as I have not bothered with footnotes. Readers will however recognize many of the references from Vatican II and elsewhere.
The starting point is the presences of Christ in the liturgy. Jesus is present in the Word, the priest, the Blessed Sacrament and the people as well as in the sacrament. It is Christ who baptizes, confirms, forgives sins, office the sacrifice, etc. It is a given, therefore, that the priest does not act in his own name or for his own purposes, He is obedient to the law by enacting the liturgy according to the texts and actions given him by the Church. His personal sanctity is not relevant for the validity of the sacramental action, although his sinfulness can impede the effectiveness of the sacrament due to scandal. Hence the formulation ex opere operato which prevents us from lapsing into the heresy of Donatism, as condemned by St Augustine.
Acting in persona Christi capitis, in the person of Christ the head, the priest represents the person of Christ in the liturgy which is different not just in degree but in essence. The reality of the People of God is given expression in the images of the Mystical Body of Christ and the Bride of Christ. Therefore, he is not seen in isolation just as the head is part of the body and the bride is inextricably joined to the groom. The priest should therefore celebrate the Mass at least one member of the faithful present. This would have been the case in the pre-conciliar liturgy as the server would always be present to respond to the prayers on behalf of the people.
When we consider the Holy Eucharist we also need to note that it has three aspects, according to Pope St John Paul II, those of: sacrifice-sacrament, presence-sacrament and communion-sacrament. I think these aspects coincide with crucifix, tabernacle and altar. In the traditional arrangement of churches, even after Vatican II, these symbols relate to each other with the altar in front with the crucifix on the wall behind it and the tabernacle located beneath or near to it. This is not a juxtaposition of symbols - it happens to be one symbol. The priest is then located, during the Eucharistic Prayer in the midst of these.
In addition to the crucifix on the wall there is for some an altar crucifix which faces towards the priest as he presides at Mass. Some see this as purely "devotional." I disagree, as I see the altar crucifix sending a message to both the priest and the congregation that the people and the priest are both facing liturgical east which is towards the Cross. We also need to be mindful that the Eucharistic Prayer is prayed to the Father and not to the congregation. The Mass goers are joined with the priest -they are not prayed to and they are not praying to him!
Having mentioned all of this, we can then look at the priest as he celebrates the Eucharistic Prayer with arms extended. To me there are two relevant postures. the first is the classic orans position with arms directed slightly forward, elbows bent, with hands separated and palms almost facing upwards. This is the classic Jewish stance of prayer. It can also be used to gesture towards the people inviting their participation in the prayer. The second position is with arms lifted to the side of the priest, elbows bent with wrists and palms facing the people. This is the image of a man crucified with his wrists attached to the cross beam, yet there is no cross.
The image of the crucifix is the image of Christ crucified but the image of the priest standing with arms in the crucifixion position is that of the Risen Christ, victor over sin and death: "Then I saw between the throne and the four living creatures and among the elders a Lamb standing as if it had been slaughtered..." (Rev 5: 6). We can also think of Moses holding out his arms in battle against the Amalekites: "Aaron and Hur held up his (Moses') hands, one on one side, and the other on the other side; so his hands were steady until the sun had set," (Ex 17: 12) We can see in this image, with the crucifix as the backdrop, an image of the risen Christ leading his people using the person of the priest. In some ways it can be seen as an Ascension moment because the people will, after the conclusion of the eucharistic action, dismissed to continue the work of the Master: "While he (Jesus) was going and they were gazing up toward heaven, suddenly two men in white robes stood by them, 'Men of Galilee, why do you stand looking up toward heaven? The Jesus, who has been taken up from you into heaven, will come in the same way as you saw him go into heaven'." (Acts 1: 10-11) The sacrament of the Eucharist is indeed sacrifice, presence and communion but also within the action of the Mass, ascension.
As a result, the priest ensures that the presence of Christ is the Eucharist is, in fact, a dynamic one. We are not stranded on Good Friday, rather we look forward also to the Second Coming of our Lord that fills us with expectation and hope, while we endure this "valley of tears." We can hear this in the embolism prayer after the Our Father: "Deliver us, Lord, we pray, from every evil, graciously grant peace in our days, that, by the help of your mercy, we may be always free from sin and safe from all distress, as we await the blessed hope and the coming of our Saviour, Jesus Christ." As a pilgrim people the congregation has before their eyes the image of victory over sin and death to draw them closer to the heavenly Father.
