Remember in Genesis, God created everything in two days, and ...no! He needed 6 days! Oh yeah...six days. And then he rested from creating everything on the 3rd day...no the 7th!...oh yeah, on Tuesday...ha! no, Saturday! Right, right...so God worked for 6 days making everything, then he took the 7th day off which we call... Saturday. Yes.
In Genesis, chapter 1 is all about creation, days 1 through 6. Then at the start of chapter 2, we read "By the seventh day God had finished the work he had been doing; so on the seventh day he rested from all his work. And God blessed the seventh day and made it holy, because on it he rested from all the work of creating that he had done." Now the Bible doesn't say the 7th day had a name. But it's the day God rested from all his work. We hear it two times in two sentences: God rested from all his work. When things are repeated in the Bible it's for emphasis: pay attention.
We know Genesis was written in....? Hebrew. Yes. The Hebrew word for 'to stop working,' or 'rest,' is Shabbath (I put it on the board). So on the 7th day God shabbathed, he rested. So what do we call that day of rest? It's almost the same in English as in Hebrew...oh! Sabbath! (Sabbath goes on the board under Shabbath) Yes, genius at work, Sabbath! So we still shabbath on the Sabbath, that is we....? Rest! Yes, we rest from our work. Since the Sabbath was the last day of the week, that's what day? Saturday. Yes, the day we go to Mass. But we go to Mass on Sunday, not Saturday! Oh yeah, Sunday is our Sabbath. Jewish people still have Sabbath on Saturday, why is Sunday our Sabbath? Because we go to Mass on Sunday. Yes, right, so why is Mass on Sunday? No guesses...OK, what day did Jesus rise from the dead? Easter Sunday! Yes, the Gospels actually tell us it was the first day of the week, Sunday. So the Christian Sabbath is on Sunday to mark the Resurrection.
By the way, in English the last day of the week is "Saturday"...who is it named after? Saturn. Yes, a Roman make-believe god. But some languages still use the word for Sabbath...como se llama Saturday en Espanol? How do you say Saturday in Spanish? Sabado. Yes (goes on the board under Sabbath), and in Greek it's Sabbato (Σάββατο), in Italian it's Sabato.
Back to resting: after all that work God did, I guess he was just exhausted, right? Ready to go to bed early? Do you think God gets tired? No.... Why not? Well, he's God. Right, God's all-powerful; a Latin word for that is omnipotent (goes on the board). God never gets tired. But I get tired, everybody I know who works hard gets worn slap out. But not God; so why did God rest, even though he wasn't tired? So we would rest when we were tired? Yes, to set an example for us. So who is the Sabbath, the rest day for? For us, for people. Yes.
And later, resting on the Sabbath became a rule, the third Commandment. In the Book of Exodus, it's long:
"Remember the Sabbath day and keep it holy. For six days you shall labour and do all your work. But the seventh day is a Sabbath to the Lord your God; you shall not do any work—you, your son or your daughter, your male or female slave, your livestock, or anyone in your town."
People were careful not to work on the Sabbath, but what's work? I mean, it's work if I go my office, but is it work to take out the trash? Or unclog a toilet? So people wanted to be sure, and in Jesus' day there were 39 rules about what was or wasn't work on the Sabbath. Jesus got into arguments with the Pharisees when he did things such as picking a handful of grain (act it out) or healing people on the Sabbath (act it out)....wasn't that doctor's work? But Jesus said, "If any of you has a sheep and it falls into a pit on the Sabbath, will you not take hold of it and lift it out? How much more valuable is a man than a sheep! Therefore it is lawful to do good on the Sabbath. The Sabbath was made for man, not man for the Sabbath."
Jesus didn't mean we can do whatever we want on Sunday. Rather we should make it a special day by doing things like paying God some attention, relaxing, having a good time with the family, or visiting someone in the hospital.
So think positively like Jesus about how to rest and keep the Lord's Day holy, not negatively like the Pharisees.