Ecclesia de Eucharistia §41

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 . 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. 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”.