The Pope himself answers this question in "Ecclesia de Eucharistia," explaining that the Church will only be able to address the challenge of the new evangelization if she is able to contemplate, and enter into a profound relationship with, Christ in the sacrament that makes his presence real.
In No. 6, the Pope is explicit in expressing the objectives of his 14th encyclical.
"I would like to rekindle this Eucharistic 'amazement' by the present Encyclical Letter, in continuity with the Jubilee heritage which I have left to the Church in the Apostolic Letter 'Novo Millennio Ineunte' and its Marian crowning, 'Rosarium Virginis Mariae,'" he says. The latter is a reference to his apostolic letter of last October on the rosary.
"To contemplate the face of Christ, and to contemplate it with Mary, is the program which I have set before the Church at the dawn of the third millennium, summoning her to put out into the deep on the sea of history with the enthusiasm of the new evangelization," he continues.
"To contemplate Christ involves being able to recognize him wherever he manifests himself, in his many forms of presence, but above all in the living sacrament of his body and his blood. The Church draws her life from Christ in the Eucharist; by him she is fed and by him she is enlightened," he adds.
Therefore, the Holy Father says: "How could I not feel the need to urge everyone to experience it ever anew?"
Lastly, in No. 10, John Paul II explains that this document was necessary because, although "the liturgical reform inaugurated by the [Second Vatican] Council has greatly contributed to a more conscious, active and fruitful participation in the Holy Sacrifice of the Altar on the part of the faithful" unfortunately "alongside these lights, there are also shadows."
"In fact, there are places where there is almost total abandonment of the practice of Eucharistic adoration," he writes. "To this must be added, in different ecclesial contexts, certain abuses that contribute to darken correct faith and Catholic doctrine on this admirable Sacrament."
"The Eucharist is too great a gift to tolerate ambiguity and depreciation," the Holy Father concludes.