Let’s turn our attention to the liturgical year according to Pope Pius XII:
151. Throughout the entire year, the Mass and the divine office center especially around the person of Jesus Christ. This arrangement is so suitably disposed that our Savior dominates the scene in the mysteries of His humiliation, of His redemption and triumph.
The principle both before Vatican II and after is that Christ is at the center of the liturgical year. There’s a good spiritual reason, namely that believers are called to union with Christ:
152. While the sacred liturgy calls to mind the mysteries of Jesus Christ, it strives to make all believers take their part in them so that the divine Head of the mystical Body may live in all the members with the fullness of His holiness. Let the souls of Christians be like altars on each one of which a different phase of the sacrifice, offered by the High priest, comes to life again, as it were: pains and tears which wipe away and expiate sin; supplication to God which pierces heaven; dedication and even immolation of oneself made promptly, generously and earnestly; and, finally, that intimate union by which we commit ourselves and all we have to God, in whom we find our rest. “The perfection of religion is to imitate whom you adore.”[Saint Augustine, De Civitate Dei, Book 8, c. 17]
There is a proper interface, then, between liturgy and spirituality. And more than an interface, a certain unified approach to the Christian life:
153. By these suitable ways and methods in which the liturgy at stated times proposes the life of Jesus Christ for our meditation, the Church gives us examples to imitate, points out treasures of sanctity for us to make our own, since it is fitting that the mind believes what the lips sing, and that what the mind believes should be practiced in public and private life.
What Pope Pius doesn’t mention is the modern development in the recognition of forming believers as active disciples in the world. And if the unity between liturgy and spirituality is sometimes cluttered, you know we have more work to do to link evangelical activity in the world with the Church’s liturgy. You can access Mediator Dei on the Vatican web site.