The Sabbath is still the Sabbath. In Israel, Friday at sundown to Saturday at sundown = the Sabbath. The last day of the week. In the holy land, you can’t even press a button for a floor in an elevator… at least that was the way it was in 95 when I was there. The elevator would stop on every floor automatically.
Sunday is the 1st day of the week. The first mass took place on resurrection day.
Lk 24:
28 So they drew near to the village to which they were going. He appeared to be going further, 29 but they constrained him, saying, “Stay with us, for it is toward evening and the day is now far spent.” So he went in to stay with them. 30 When he was at table with them, he took the bread and blessed, and broke it, and gave it to them. 31 And their eyes were opened and they recognized him; and he vanished out of their sight. 32 They said to each other, “Did not our hearts burn within us while he talked to us on the road, while he opened to us the scriptures?” 33 And they rose that same hour and returned to Jerusalem; and they found the eleven gathered together and those who were with them, 34 who said, “The Lord has risen indeed, and has appeared to Simon!” 35 Then they told what had happened on the road, and how he was known to them in the breaking of the bread."
That said,
While the following scripture, doesn’t say
mass
Eucharist
Sunday
We can clearly see what they are celebrating, on the “Day” and the consequences if one deliberately misses mass on Sunday, After receiving knowledge of the truth
Heb 10:
22 let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. 23 Let us hold fast the confession of our hope without wavering, for he who promised is faithful; 24 and let us consider how to stir up one another to love and good works, 25 not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near.
26 For if we sin deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful prospect of judgment, and a fury of fire which will consume the adversaries. 28 A man who has violated the law of Moses dies without mercy at the testimony of two or three witnesses. 29 How much worse punishment do you think will be deserved by the man who has spurned the Son of God, and profaned the blood of the covenant by which he was sanctified, and outraged the Spirit of grace? 30 For we know him who said, “Vengeance is mine, I will repay.” And again, “The Lord will judge his people.” 31 It is a fearful thing to fall into the hands of the living God."
They are celebrating the Eucharist on Sunday. To deliberately miss mass, on Sunday then, draws those consequences mentioned after one becomes knowledgeable of the truth