The following is an answer to a question raised in an Orthodox email forum, answered by Fr. Alexander Lebedeff.
I recently read a post in which the author stated that a thorough answer had never been given regarding the practice of laymen lifting up their arms during the Anaphora, or saying three "Amens" after the Epiclesis.
I'll try to clarify the issue, at least from my point of view.
I had previously written that praying with both arms upraised was the prerogative of the Priest, following the simple paradigm: the Priest prays (at appointed times) with both arms raised; the Deacon prays with one arm raised, and the faithful laypeople pray without raising their arms.
This paradigm is one that is reflected in many other areas. At the service of ordination, the candidate for the diaconate bows one knee before the altar table; the candidate for Priesthood kneels on both knees, as a symbol of the extra (double) burden of the Priesthood. The Deacon wears the orarion on one shoulder. The Priest's stole (epitrachelion) is the same orarion, just worn over both shoulders, again indicating his extra spiritual responsibility. The Deacon's orarion even has only one row of fringe, while the Priest's stole always has two, for the same reason. The chain of the cross of a Priest or Bishops, in contrast with the chain of the baptismal (on-the-body) cross of a layman has an extra loop that hangs down in the back, symbolizing the extra burden of the Priest, who carries not only his own sins, but the sins of his flock on himself.
So, allowing laypeople to raise their both arms is presuming upon the prerogative of the Priest. It cannot be considered an acceptable expression of fervor, since even the Priest is explicitly cautioned by the rubrics not to make any spontaneous expressions of fervor, explicitly including raising of arms during non-specified times in the services. If this rubric applies to Priests, it certainly should apply to laymen, as well.
Similarly, the proclaiming aloud of three "amens" after the epiclesis is another uncalled-for expression of fervor, meaning it is not specified in the rubrics of the service. The service books state clearly that the three "Amens" are said by the Deacon. It does not say: "and the people say—amen, amen, amen."
Again, this is an example of laypeople usurping the prerogative of the Deacon, who participates actively in the consecration of the Holy Gifts, and gives both the invitations ("Bless, Master, the Holy Bread." etc.) and the responses, including the "Amens." It would be inappropriate for the altar servers to participate in these responses, even though they are right there and can see and hear what is occurring. During the epiclesis, the choir is singing the solemn hymn "We sing unto Thee...", the Royal Doors are closed, and the faithful stand in silent prayer that should not be interrupted by any amens, however well-intentioned. In order to even know when the exact moment to say these amens occurs, the congregation would have to hear the words that the Priest is supposed to pronounce quietly during the singing of the hymn. Either the Priest would have to say them quite loudly, drowning out the singing, or the singing would have to stop so that you could hear what the Priest was saying. Both would be a violation of the order of the service (as is any reading aloud by a Priest of any prayer meant to be read quietly or silently).
Actually, there are a variety of dynamics indicated in the services for prayers. Some are said quietly (in a low voice), some are said loudly (in a great voice), some are said silently (no voice). We should humbly defer to the holy authors of these services and follow their directions. Whenever we want to introduce something "of our own," we not only violate the service rubrics, but we violate the unity of the church.
All such "unique" practices should be patiently and lovingly eliminated.
Source: http://orthodoxinfo.com/praxis/arms_amen.aspx