Encyclical Letter on the Holy Eucharist - Parts 41 & 42

41. The Eucharist's particular effectiveness in promoting communion is one of the reasons for the importance of Sunday Mass. I have already dwelt on this and on the other reasons which make Sunday Mass fundamental for the life of the Church and of individual believers in my Apostolic Letter on the sanctification of Sunday Dies Domini.⁸⁶ There I recalled that the faithful have the obligation to attend Mass, unless they are seriously impeded, and that Pastors have the corresponding duty to see that it is practical and possible for all to fulfil this precept.⁸⁷ More recently, in my Apostolic Letter Novo Millennio Ineunte, in setting forth the pastoral path which the Church must take at the beginning of the third millennium, I drew particular attention to the Sunday Eucharist, emphasizing its effectiveness for building communion. “It is” – I wrote – “the privileged place where communion is ceaselessly proclaimed and nurtured. Precisely through sharing in the Eucharist, the Lord's Day also becomes the Day of the Church, when she can effectively exercise her role as the sacrament of unity”.⁸⁸ 

42. The safeguarding and promotion of ecclesial communion is a task of each member of the faithful, who finds in the Eucharist, as the sacrament of the Church's unity, an area of special concern. More specifically, this task is the particular responsibility of the Church's Pastors, each according to his rank and ecclesiastical office. For this reason the Church has drawn up norms aimed both at fostering the frequent and fruitful access of the faithful to the Eucharistic table and at determining the objective conditions under which communion may not be given. The care shown in promoting the faithful observance of these norms becomes a practical means of showing love for the Eucharist and for the Church.