The fundamental ideas of the liturgical constitution belong to the core theological content of Vatican II: pastoral bearing, connection between liturgy and ecclesiology, Church as a sacrament, and history of salvation. … Losing the connection between the liturgical reform and the rest of the theology of Vatican II means leaving the other documents of the council without their primary and ultimate framework of solemn expression in the Church, the liturgy. …
The philosopher and friend of Paul VI, Jean Guitton, asked the pope why he did not concede “the Missal of 1962” to Lefebvre and his followers. the pope replied:
Never. This Mass so called of Saint Pius V, the one we see in Econe, becomes the symbol of the condemnation of the council. I will not accept, under any circumstances, the condemnation of the council through a symbol. Should this exception to the liturgy of Vatican II have its way, the entire council would be shaken. And, as a consequences, the apostolic authority of the council would be shaken.
— Massimo Faggioli, True Reform: Liturgy and Ecclesiology in Sacrosanctum Concilium (Liturgical Press, 2012), 149-150