Ratzinger states his purpose for writing the book: to assist the renewal of the understanding of the liturgy by building on what Guardini wrote in his 1918 book The Spirit of the Liturgy, updating it for a contemporary setting, hoping to encourage a liturgical movement “toward the right way of celebrating the liturgy, inwardly and outwardly.”  [Later, we will get into what the right way is.]
He mentioned that one of the difficulties that had crept into the Mass prior to the Second Vatican Council was the “instructions for and the forms of private prayer,”  that distracted the faithful from seeing the beauty of the liturgy (which he likens to a fresco). The fresco, he states “had been preserved from damage [in Guardini’s time], but it had been almost completely overlaid with whitewash by later generations.”  [Those private devotions distracted the people and covered over the beauty of what was happening before them.]
Guardini’s book “helped us to rediscover the liturgy in all its beauty, hidden wealth, and time-transcending grandeur”  and inspired a Liturgical Movement in Germany, which helped to preserve its beauty despite the white-washing. The Second Vatican Council again showed us the beauty of the liturgy, but
since then the fresco has been endangered by climatic conditions as well as by various restorations and reconstructions. In fact it is threatened with destruction, if the necessary steps are not taken to stop these damaging influences. 
I’m sure that many of us have been witnesses to destruction of elements of the beauty in the Mass: art, architecture, music, and (even more sadly) reverence. I will not dwell on them here because he treats them later, but I cannot stress enough the importance that we Catholics need to return to a sense of beauty, reverence, and majesty in our liturgies, for the sake of the souls in the pews. We need an inspiring liturgy–one that doesn’t just speak to us where we’re at (or worse: tries to entertain us), but one that draws us up out of our daily life and inspires us to look toward God and order our whole lives accordingly. Pope Benedict XVI has not changed his views since becoming pope. He has not made many top-down liturgical commands, rather he has led by example–restoring, in the Masses he offers, the beauty that had been damaged. He gave us Anglophones an excellent example of this when he celebrated Mass in Westminster Cathedral. Below is a video excerpt from that Mass. Note how beautiful and inspiring everything is and how different it is from our everyday lives–Mass provides us that time to step away from everyday life and focus on what is really important: God. Ask yourself: “how can my parish (with what resources it has) offer Masses more like that?”
I pray that God will bless me with a better understanding of this book, and the liturgy, and that what little work I am able to do will be done with love, and will help preserve the beauty of the fresco. I pray, too, that you, dear readers, will be inspired to give greater glory to God–particularly in the liturgy.
Trying to glorify God in my work,