When I was a full time missionary in the MTC in Provo (January-March ’82), we were taught to keep our left arms and hands at our side. That is, we were specifically told not to bend our left arm behind our backs, as do some worldly armies. We were told that we were a “Royal Army” and should not mimic any army of the world. Has this recommendation changed in our days? Is it now recommended to hold our left arms behind our backs when passing the Sacrament?
The recommendation remains the same, but says nothing of army postures. From the Church Handbook of Instruction volume 2, 20.4.1 Sacrament, General Guidelines:
The passing of the sacrament should be natural and unobtrusive, not rigid or overly formal. Those who pass the sacrament should not be required to assume any special posture or action, such as holding the left hand behind the back. The process of passing the sacrament should not call attention to itself or detract from the purpose of the ordinance.
The principle at play is that “deacons or other priesthood holders pass the bread to the congregation in a reverent and orderly manner” but not so “orderly” as to be “rigid or overly formal”. Nothing should be “distracting from the sacred nature of the ordinance.” Ultimately, it is the bishop’s duty to determine whether deacons need correction individually or as a quorum (or whether it’s a non-issue), as he “ensures that priesthood holders have a reverent, dignified manner as they participate in this ordinance.”