from:
ewtn.com/expert/answers/orans_posture.htm
"Our Father. The intention for lay people using the Orans position at this time is, I suppose, that we pray
Our Father, and the unity of people and priest together is expressed by this common gesture of prayer. Although this gesture is not called for in the rubrics, it does at least seem, on the surface, to
not be in conflict with the sacramental sign system at the point when we pray
Our Father. I say on the surface, however, since while lay people are doing this the deacon, whose postures
are governed by the rubrics, may not do it. So, we have the awkward disunity created by the priest making an appropriate liturgical gesture
in accordance with the rubrics, the deacon
not making the same gesture
in accordance with the rubrics,
some laity making the same gesture as the priest
not in accordance with the rubrics, and other laity not making the gesture (for various reasons, including knowing it is not part of their liturgical role). In the end, the desire of the Church for liturgical unity is defeated."