I know that Mass on the evening before Sunday fills the obligation for attending Mass on Sunday (or another holy day for that matter). My girlfriend, who is protestant, asked me why? I did not know how to answer her. Does somebody know why this is?
I believe it is because the Sabbath begins at sundown.
I htink there are lots of reasons … the definition of a day from our Judeo-Christian roots being Evening - then Morning probably being one of the best [see Genesis, etc]…
However, this is how I explain it - using the commision to pray unceasingly … and the Church’s daily prayer practice …
If you look at the Litugy of the Hours [Divine Office], there is no Saturday Evening Prayer … you find Sunday Evening Prayer I, followed by Sunday Morning Prayer and then Sunday Evening Paryer II … so in liturgical time, Sunday is longer … much longer
and Saturday night non-existant
The simple answer is: Because Canon Law allows it so:
Can. 1247 On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass.
Can. 1248 §1. A person who assists at a Mass celebrated anywhere in a Catholic rite either on the feast day itself or in the evening of the preceding day satisfies the obligation of participating in the Mass.
If you mean to ask *Why does Canon Law allow it so? *the answer is more complicated.