Maria, I am delighted that you are reading and enjoying C. S. Lewis. He is a remarkable writer and Christian theologian.
Pope Pius XII's encylical Mystici Corporis Christi is not addressing liturgical abuses. During the first four decades of the 20th century, Catholic theology had rediscovered the Pauline understanding of the Church as the mystical body of Christ. Some theologians took this in directions that were deemed problematic by some. In his encyclical the Pope sought to present an understanding of the body of Christ that was fully faithful to Catholic ecclesiology. Widescale liturgical abuse simply was not a problem in the Catholic Church at this time, and whatever little experimentation may have been occurring was restricted and hardly needed to be addressed by an encyclical. Catholic pastors simply did not have the freedom, unlike their Anglican counterparts, to experiment with the Mass. That all would come much later.
At the time Lewis wrote his Letters to Malcolm, the winds of liturgical change were blowing in the Church of England. Some (many?) wanted a liturgy composed in a contemporary idiom. Lewis was opposed to this. He did not believe that a committee could create a liturgy that could begin to compare to the beauty and magnificence of traditional Book of Common Prayer. The BCP was largely the work of one poetic genius, Thomas Cranmer. Such geniuses do not appear very often. Lewis was also opposed to liturgical tinkering, a tinkering that Anglican pastors were famous for. Lewis valued stability. One is not dancing as long as one has to think about the steps. It is only when one has internalized the steps that one can truly dance. The same applies to praying the liturgy, so Lewis believed.
Lewis did enjoy a friendship at Oxford with the lay Orthodox theologian Nicholas Zernov. He also delivered one or two talks to the Fellowship of St Alban and St Sergius. in the late 50s Lewis and Joy visited Greece and attended the Divine Liturgy during their visit. Lewis's biographer, George Sayers, writes: "Whenever the subject came up between us, [Lewis] said that he preferred the Orthodox liturgy to either the Catholic or Protestant liturgies. He was also impressed by the Greek Orthodox priests, whose faces, he thought, looked more spiritual than those of most Catholic or Protestant clergy." But I know of no evidence that suggests that Lewis ever contemplated becoming Orthodox.
But that being said, I happily acknowledge that Lewis's mere Christianity is compatible with Orthodoxy in many ways. But such was the Anglicanism of his day.
In Pope Pius XII's encyclical
Mystici Corporis Christ, which I have read several times and have studied under the Dominicans at the Dominican University in San Rafael,
diocesan liturgical committees are mentioned. Again, I ask: Why were liturgical committees apparently ordered to be set up in all dioceses by Pius XII if they were not to advance the study and amending of the Mass to make the Mass more meaningful and fruitful for the laity and for the clergy? These liturgical committees encouraged laity participation. I can remember back in 1956 through 1960, pre-Vatican II times, that both priests and nuns were encouraging us to read a translation of the Mass and not to pray the Rosary as our adult relatives and grandparents were doing. We were encouraged to bring our black Sunday missals to Mass. The nuns had extra copies if we forgot our own missals, but we were chastised if we did forget. I can also remember my aunt and grandmother having a fit over the Rosary. They questioned my Catholic education, and gave me a beautiful Rosary for my confirmation in 1960.
Yes, the encyclical discusses the Mystical Body of Christ, but Pope Pius XII most correctly states that we experience the Mystical Body of Christ most completely during the celebration of the Holy Eucharist. This was a profound Orthodox statement.
Dominicans of the 1950s and 1960 were also encouraging the laity to realize the treasure of the Divine Liturgy. The Church was instituted to perpetuate the Eucharist as said in that Dominican Prayer composed by St. Thomas Aquinas:
O sacrum convivium,
in quo Christus súmitur;
recólitur memória Passionis eius;
mens implétur grátia:
et futúrae glóriae nobis pignus datur.
Alleluia. Alleluia. Alleluia.
Dominican Prayer Book (4th Revised Edition), Curia Generalizia, O.P. Rome, 1962, p. 120
(Translation)
O Sacred Banquet in which Christ is received,
The memory of His passion is renewed,
The mind is filled with grace,
and a pledge of future glory is given to us.
V. Thou didst give them bread from heaven.
R. Containing in itself all sweetness.
Let us pray:
O God, Who under a wonderful Sacrament has left us a memorial of Thy Passion:
grant us, we beseech Thee, so to venerate the sacred mysteries of Thy Body and Blood,
that we may ever feel within ourselves the fruit of Thy Redemption:
Who livest and reignest for ever and ever.
R. Amen
Dominican Prayer Book (4th Revised Edition), Curia Generalizia, O.P. Rome, 1962, p. 322
Since Lewis experienced our Divine Liturgy in Greece, no wonder he did not convert to Catholicism. With our glorious Divine Liturgy which focuses on Christ's Holy Resurrection, we are taken up to heaven to celebrate the eternal Feast of the Lamb with the angels and saints surrounding us as we put aside all earthly cares. How could he not want that.