The moral obligation to participate in the eucharistic sacrifice on Sundays dates from the very beginning of Christianity, although it did not become a definite law of the Church until the fourth century. 
Read more from Manuel Garrido, O.S.B.
 

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Catholics are instructed to attend Mass and enjoy adequate rest on Sundays (see Catechism of the Catholic Church 2180-2188). This is not optional. However, in our modern society filled with packed schedules and stacks of bills, many Christians treat Sunday like just another day.  Read more from Nicholas LaBanca