A question I recently received asked me when the Church changed its rules about going to Mass on Sunday: is it still an obligation?
 

The short answer is:  Yes!

The long answer:  One of the precepts of the Church is that all Catholics MUST actively participate in the Mass each and every Sunday and every Holy Day of obligation.  So what happens if someone misses Mass?  Is it a sin?
 
It depends.  If one is very ill (flu, paralyzed, heart attack, etc.) and they either cannot or should not go to Church); if the weather is so treacherous that one cannot or should not risk driving to Church: no, it is NOT a sin to miss Mass, but one should do one’s best to go to Mass at the next possible convenience (say a Monday or Tuesday Mass.)

If you have other commitments (such as a sporting event...even the Green Bay Packers), or you’re tired because you stayed up late, or you’re just not in the mood..YOU STILL HAVE TO GO.  What are the consequences?  Only God knows what is truly in your heart—and HE DOES KNOW—-and if you choose some other god (notice the small “g”) like sports or shopping or working et cetera, you have committed a Mortal Sin—a Serious Sin—and you need to go to Confession with the intent of NOT DOING THAT AGAIN.

 God is the one who told us to keep holy the Sabbath; the Catholic Church tells us how (by going to Mass.)  See the Catechism of the Catholic Church, #2041.

Precepts of the Catholic Church