It will be the 14th encyclical written by the Holy Father in his close to 25-year pontificate.
The real presence of Christ in the sacrament of the Eucharist brings together all of the writings of John Paul II's pontificate, which began with the March 1979 encyclical on Jesus Christ, entitled "Redemptor Hominis," the Vatican sources explained.
In his apostolic letter "Novo Millennio Ineunte," the Pope explains the importance of the Eucharist.
"We are entering a millennium which already shows signs of being marked by a profound interweaving of cultures and religions, even in countries which have been Christian for many centuries," he explained in No. 36 of the letter. "In many regions Christians are, or are becoming, a 'little flock.'"
"This presents them with the challenge, often in isolated and difficult situations, to bear stronger witness to the distinguishing elements of their own identity," he adds. "The Sunday Eucharist, which every week gathers Christians together as God's family round the table of the Word and the Bread of Life, is also the most natural antidote to dispersion."
In recent years the Pope has spoken about the importance of Sunday Mass in many addresses. He highlighted this importance in his 1998 apostolic letter "Dies Domini" (Day of the Lord).