Missing mass is a mortal sin and can send one to hell, that is works.. receiving communion gives grace..that is works ...
Remember what Jesus said to the holy men of the Jews? He called them vipers and said they were sons of the devil.. all they did was follow the "rules" Works
BTW Trent chose words CAREFULLY and chose to use the BIBLICAL word anathema ...
1Co 16:22 If any man love not the Lord Jesus Christ,let him be Anathema Maranatha.
Strongs G331 in the following manner: accursed (4x), anathema (1x), bind under a great curse (with G332) (1x).
The most frequent translation in the NT is "cursed,and accursed.. not "excommunicated" that is just Rome trying to soften sending people to hell :)