But the question is, where did Eucharisticum Mysterium get its “idea” for receiving Holy Communion “either kneeling or standing”? The posture is not mentioned in Sacrosanctum Concilium, nor any document between it and EM. When it says “the custom of the Church”, is it talking about the Latin Rite Church, or the entire Catholic Church? In other words, is it mixing Traditions, and if so, why?
The idea for standing came out of the Consilium that wrote the New Mass. It was made acceptabe with the Consilium instruction Eucharisticum Mysterium
adoremus.org/eucharisticummysterium.html
- The Way of Receiving Communion
a) In accordance with the custom of the Church, Communion may be received by the faithful either kneeling or standing. One or the other way is to be chosen, according to the decision of the episcopal conference, bearing in mind all the circumstances, above all the number of the faithful and the arrangement of the churches. The faithful should willingly adopt the method indicated by their pastors, so that Communion may truly be a sign of the brotherly union of all those who share in the same table of the Lord.
b) When the faithful communicate kneeling, no other sign of reverence toward the Blessed Sacrament is required, since kneeling is itself a sign of adoration.
When they receive Communion standing, it is strongly recommended that, coming up in procession, they should make a sign of reverence before receiving the Blessed Sacrament. This should be done at the right time and place, so that the order of people going to and from Communion may not be disrupted."
This document also allowed communion under both kinds. It would be difficult to receive from the Chalice kneeling if front of a communion rail which still existed at the time, so in my opinion, they had to allow the option of standing to receive from the Chalice. Over time standing has become the norm for both the host and chalice in the New Mass especially after the communion rails were removed in the majority of Churches.
In Father Bugnini’s book* Reform of the Liturgy* he shows that there was some opposition from Cardinal Larraona, a member of the Consilium and president of the pre-council commission that wrote the Constitution. The Cardinal said, “in order to protect orthodox belief in the real presence, reception of communion while standing be allowed only as an exception” He then states that the Canon should not be said aloud, “since this would be the first step of the vernacular into the Canon”
Bugnini states, “These ideas were unacceptable”