It says to keep the Sabbath. For Catholics, that means going to Mass on all Sundays and Holy Days of Obligation. “Mortal sin” means a sin that kills whatever grace is your soul, not that your body will die then and there.
“It says to keep the Sabbath. For Catholics, that means going to Mass on all Sundays and Holy Days of Obligation.”
The Sabbath is specifically Saturday, which is the day the Lord rested. We are not bound by the law, so Sabbath keeping isn’t necessary for salvation, though many honor it. However, it doesn’t just transform into Sunday and other days. If that was the case, you’d redefine the word Sabbath and have them refer to all those days, instead of calling them by something else. These are distinct holy days. I think the Jews would be quite upset at the idea that a word has so little meaning.
Whatever the case, there is no binding doctrine on having one day or another as Holy. Romans 14 actually teaches that such a focus on particular days in the first place is in vain. Augustine, himself, actually celebrating the Lord’s Supper everyday, and not on Sunday. And I would regard that we all have a liberty to worship God how we please, whenever we want, similarly.
We are not under law, we are under grace.
Now, as for grace. Grace isn’t an inanimate object that can be destroyed or renewed. Grace is, by definition, the free gift and favor of God on the undeserving sinner, regardless of our works:
Rom 3:23-24 For all have sinned, and come short of the glory of God; (24) Being justified freely by his grace through the redemption that is in Christ Jesus:
Rom_5:15 But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.
It is given to us before the foundation of the world, predestinated according to His own desire to give it to us despite our works:
2Ti_1:9 Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began,
Rom 9:11-16 (For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth;) (12) It was said unto her, The elder shall serve the younger. (13) As it is written, Jacob have I loved, but Esau have I hated. (14) What shall we say then? Is there unrighteousness with God? God forbid. (15) For he saith to Moses, I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion. (16) So then it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy.
Salvation, as the Apostle concludes, is not on him that willeth or him that runneth, but on the sovereign mercy of God who chooses us to not only believe in him, but to produce fruit; this choice is purely the choice of God:
Joh_15:16 Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.