That being said, I will reproduce the first post here. It is about the decree Quo actuosius, by which the formulary for the distribution of Holy Communion was changed to simply "The Body of Christ. / Amen."
252. SC RITES, Decree Quo actuosius, promulgating a new formulary for the distribution of communion, 25 April 1964: AAS 56 (1964) 337-338.And here is the commentary I made on this document:
In order that the people may more actively and beneficially take part in the sacrifice of the Mass and profess their faith in the eucharistic mystery in the very act of receiving communion, numerous requests have been submitted to Pope Paul VI for a more appropriate formulary for the distribution of communion.
Graciously welcoming such requests, the Pope has established that in the distribution of communion, in place of the formulary now in use, the priest simply to say: The body of Christ and the people are to answer: Amen, then receive communion. This is to be followed whenever communion is distributed, both within and outside Mass.
All things to the contrary notwithstanding, even those worthy of special mention.
The previous formulary for receiving Communion had been the following, said by the priest:
Corpus Dómini nostri Jesu Christi custódiat ánimam tuam in vitam aetérnam. Amen.
The communicant did not make a reply.
The formula which replaced it was:
Priest: Corpus Christi.
The previous form was a blessing said by the priest to each one receiving Communion: "May the Body of Our Lord Jesus Christ preserve your soul unto life everlasting. Amen."
From my point of view, the previous form could have been adjusted only slightly to facilitate the "active participation" (which here apparently means saying something) of the faithful:
Priest: Hoc Corpus Dómini nostri Jesu Christi custódiat ánimam tuam in vitam aetérnam.
The priest is now saying, in effect, "May this, the Body of our Lord Jesus Christ, preserve your soul unto life everlasting" to which the communicant responds "Amen". It is still a blessing, yet it incorporates a profession of faith from the communicants: no longer is "some" Body of our Lord Jesus Christ (which is not identified with the Host being received) preserving their soul, but this which is the Body of our Lord Jesus Christ.